Memory device to execute read operation using read target voltage

ABSTRACT

A memory device includes first and second memory strings, first and second word lines and a controller. The first memory string includes first and second memory cells, a first select transistor, a second select transistor, and a third select transistor between the first and second memory cells. The second memory string includes third and fourth memory cells, a fourth select transistor above the third memory cell, a fifth select transistor below the fourth memory cell, and a sixth select transistor between the third and fourth memory cells. The first word line is electrically connected to gates of the first and third memory cells. The second word line is electrically connected to gates of the second and fourth memory cells. The controller is configured to execute a read operation on one of the memory cells, the read operation including a first phase and a second phase after the first phase.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.15/445,985, filed on Mar. 1, 2017, which is based upon and claims thebenefit of priority from Japanese Patent Application No. 2016-181534,filed Sep. 16, 2016, the entire contents of each of which areincorporated herein by reference.

FIELD

Embodiments described herein relate generally to a memory device.

BACKGROUND

A NAND type flash memory in which memory cells are arranged in athree-dimensional manner is known.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a memory system including amemory device of an embodiment.

FIG. 2 is a block diagram illustrating an example of an internalconfiguration of the memory device of the embodiment.

FIG. 3 is a circuit diagram illustrating an example of a memory cellarray of the memory device of the embodiment.

FIG. 4 is a circuit diagram illustrating an example of a row controlcircuit of the memory device of the embodiment.

FIG. 5 is a perspective view of the memory cell array of the memorydevice of the embodiment.

FIG. 6 is a plan view of the memory cell array of the memory device ofthe embodiment.

FIG. 7 is a sectional view of the memory cell array of the memory deviceof the embodiment.

FIG. 8 is a sectional view of a memory string in the memory cell arrayof the memory device of the embodiment.

FIG. 9 is a diagram illustrating a relationship between thresholdvoltage of the memory cell and data.

FIG. 10A is a schematic diagram of a first example for explaining arelease process carried out in the memory device of the embodiment.

FIG. 10B is a schematic diagram of a second example for explaining arelease process carried out in the memory device of the embodiment.

FIG. 11 is a flowchart for explaining an operation example of the memorydevice of the embodiment.

FIGS. 12-16 are each a timing chart illustrating an operation example ofa memory device according to a first embodiment.

FIGS. 17-18 are each a timing chart illustrating an operation example ofa memory device of a second embodiment.

FIG. 19 is a timing chart illustrating an operation example of a memorydevice of a third embodiment.

FIG. 20 is a timing chart illustrating an operation example of a memorydevice of a fourth embodiment.

FIGS. 21-22 are each a timing chart illustrating an operation example ofa memory device of a fifth embodiment.

FIGS. 23-24 are each a timing chart illustrating an operation example ofa memory device of a sixth embodiment.

FIG. 25 is a timing chart illustrating an operation example of a memorydevice of a seventh embodiment.

FIG. 26 is a timing chart illustrating an operation example of a memorydevice of an eighth embodiment.

FIGS. 27-28 are each a timing chart illustrating an operation example ofa memory device of a ninth embodiment.

FIGS. 29-30 are each a timing chart illustrating an operation example ofa memory device of a tenth embodiment.

FIG. 31 is a diagram illustrating a modification example of the memorydevice of the embodiment.

FIGS. 32A and 32B are diagrams illustrating a modification example ofthe memory device of the embodiment.

FIG. 33 is a diagram illustrating a modification example of the memorydevice of the embodiment.

FIGS. 34A to 34F are diagrams illustrating a modification example of thememory device of the embodiment.

DETAILED DESCRIPTION

Operation characteristics of a memory device are improved according toembodiments.

In general, according to an embodiment, a memory device includes a firstmemory string including a first memory cell, a second memory cell, afirst select transistor above the first memory cell, a second selecttransistor below the second memory cell, and a third select transistorbetween the first memory cell and the second memory cell; a secondmemory string including a third memory cell, a fourth memory cell, afourth select transistor above the third memory cell, a fifth selecttransistor below the fourth memory cell, and a sixth select transistorbetween the third memory cell and the fourth memory cell; a first wordline electrically connected to a gate of the first memory cell and agate of the third memory cell; a second word line electrically connectedto a gate of the second memory cell and a gate of the fourth memorycell; and a controller configured to execute a read operation on one ofthe memory cells, the read operation including a first phase and asecond phase after the first phase, wherein when a read target is one ofthe first memory cell and the second memory cell, during the firstphase, a first voltage is applied to one of the first select transistorand the second select transistor, the third select transistor, and oneof the fourth select transistor and the fifth select transistor, and asecond voltage lower than the first voltage is applied to the sixthselect transistor and the other one of the fourth select transistor andthe fifth select transistor, and during the second phase, the firstvoltage is applied to the first select transistor, the second selecttransistor and the third select transistor, and the second voltage isapplied to the fourth select transistor, the fifth select transistor,and the sixth select transistor.

Hereinafter, with reference to the drawings, the present embodiment willbe described in detail. In the following description, constituentelements having the same function and configuration are given the samereference numerals.

In the following respective embodiments, if constituent elements withreference signs (for example, word lines WL, bit lines BL, and variousvoltages and signals) have numbers/letters at ends thereof fordifferentiation. If they are not to be distinguished from each other,the constituent elements are described with reference signs with thenumbers/letters omitted at the ends thereof.

Embodiments (1) First Embodiment

With reference to FIGS. 1 to 16, a memory device according to anembodiment will be described.

(a) Configuration

With reference to FIGS. 1 to 9, a description will be made of aconfiguration example of the memory device of the embodiment.

FIG. 1 is a diagram illustrating a memory system including the memorydevice of the present embodiment.

As illustrated in FIG. 1, a memory system 9 including the memory deviceof the present embodiment includes a storage device 500 and a hostdevice 600.

The host device 600 is coupled to the storage device 500 via, forexample, a connector, a cable, wireless communication, or the Internet.The host device 600 requests the storage device 500 to perform writingof data or erasing of data or reading of data.

The storage device 500 includes a memory controller 5, and a memorydevice (semiconductor memory) 1.

The memory controller 5 causes the memory device 1 to perform anoperation corresponding to a request from the host device 600.

The memory controller 5 includes, for example, a processor (CPU), aninternal memory (for example, a DRAM), a buffer memory (for example, anSRAM), and an ECC circuit. The processor controls the entire operationof the memory controller 5. The internal memory temporarily holds aprogram (software/firmware) and management information (managementtable) of the storage device/the memory device. The buffer memorytemporarily holds data transmitted and received between the memorydevice 1 and the host device 600. The ECC circuit detects an error indata read from the memory device 1, and corrects the detected error.

The memory device 1 stores data. The memory device 1 performs writing ofdata, reading of data, and erasing of data based on commands (requestsfrom the host device 600) from the memory controller 5.

The memory device 1 is, for example, a NAND type flash memory. Thestorage device 500 (or the memory system 9) including the flash memory 1is, for example, a memory card (for example, an SD™ card or an eMMC™), aUSB memory, or a solid state drive (SSD).

Various signals are transmitted and received between the NAND type flashmemory 1 and the memory controller 5. For example, a chip enable signalCEn, a command latch enable signal CLE, an address latch enable signalALE, a write enable signal WEn, a read enable signal REn, and a writeprotect signal WPn are used as control signals based on a NAND interfacestandard between the flash memory 1 and the memory controller 5.

The signal CEn is used to enable the flash memory 1. The signal CLE andthe signal ALE are used to respectively notify that signals on I/O linesIO (IO1 to IO8) are a command and an address signal.

The signal WEn and the signal REn are used to given an instruction forinputting and outputting of signals using, for example, eight I/O linesIO. The signal WPn is used to set the flash memory 1 in a protectionstate, for example, when a power source is turned on and off.

A ready/busy signal RBn is generated based on an operation state of theflash memory 1, and is transmitted to the memory controller 5. Thesignal RBn is used to notify the memory controller 5 whether the flashmemory 1 is in a ready state (a state of being ready to receive acommand from the memory controller 5) or a busy state (a state of notbeing ready to receive a command from the memory controller 5). Forexample, the signal RBn is at an “L” level (busy state) while the flashmemory 1 is performing an operation such as reading of data, and goes toan “H” level (ready state) if such an operation is completed.

FIG. 2 is a block diagram illustrating an internal configuration of thememory device (for example, a NAND type flash memory) of the presentembodiment.

As illustrated in FIG. 2, the NAND type flash memory 1 includes a memorycell array 11, a row control circuit 12, a sense amplifier circuit 13, adata holding circuit 14, a source line driver 15, a well driver 16, aninput/output circuit 17, a voltage generation circuit 18, a sequencer19, and the like.

The memory cell array 11 includes a plurality of blocks BK (BK0, BK1,BK2, . . . ). Each of the blocks BK includes a plurality of string unitsSU (SU0, SU1, SU2, . . . ). Each of the string units SU includes aplurality of NAND strings (memory cell strings) 111. Each of the NANDstrings 111 includes a plurality of memory cells. An internalconfiguration of the memory cell array 11 will be described later.

The row control circuit 12 controls rows (for example, word lines) ofthe memory cell array 11.

The row control circuit 12 includes a plurality of address decoders 120,a plurality of switch circuits 121, and a driver 129. A single addressdecoder 120 corresponds to a single block BK. A single switch circuitcorresponds to a single block BK. The address decoders 120 decodeaddresses from the memory controller 5. The switch circuits 121 enableblocks BK corresponding to addresses, and disable other blocks BK basedon decoding results in the address decoders 120. The driver 129 suppliesvoltages corresponding to enabling/disabling of the blocks BK to therespective blocks BK via the switch circuits 121.

The sense amplifier circuit 13 senses and amplifies a signal (data)which is output to a bit line in the memory cell array 11 during readingof data. For example, the sense amplifier circuit 13 senses theoccurrence of a current in the bit line (or a wiring connected to thebit line) or a change in a potential of the bit line, as a signal fromthe memory cell. Based on such sensing, the sense amplifier circuit 13reads data held in the memory cell. The sense amplifier circuit 13controls a potential of the bit line according to data to be writtenduring writing of data. The sense amplifier circuit 13 includes senseamplifier units 131 which control sensing in respective bit lines, andthe bit lines.

The data holding circuit (for example, a page buffer circuit) 14temporarily holds data which is output from the memory cell array 11, ordata (data from the memory controller 5) which is input to the memorycell array 11.

The source line driver 15 controls potentials of source lines in thememory cell array 11. The well driver 16 controls a potential of a wellregion in the memory cell array 11.

The input/output circuit 17 functions as an interface circuit of theabove-described various control signals from the memory controller 5 andthe I/O lines IO1 to IO8. The voltage generation circuit 18 generatesvarious voltages used for an operation of the memory cell array 11.

The sequencer 19 controls the entire operation of the flash memory 1.The sequencer 19 controls an internal operation of the flash memory 1based on control signals and commands which are transmitted and receivedbetween the memory controller 5 and the flash memory 1.

Circuit Configuration of Memory Cell Array

With reference to FIGS. 3 and 4, a description will be made of anexample of an internal configuration of the memory cell array in theflash memory of the present embodiment.

FIG. 3 is an equivalent circuit diagram of a single block in the memorycell array 11. In the memory cell array 11 of the NAND type flashmemory, the block BK is an erasing unit of data. However, an erasingoperation on the memory cell array 11 may be performed in the unit(storing area) smaller than the block. The erasing operations disclosedin U.S. patent application Ser. No. 12/679,991, filed on Mar. 25, 2010,entitled “nonvolatile semiconductor memory device and manufacturingmethod thereof,” and U.S. patent application Ser. No. 12/532,030, filedon Mar. 23, 2009, entitled “semiconductor memory and manufacturingmethod thereof,” both of which are incorporated by reference herein, maybe used in the embodiments.

As illustrated in FIG. 3, in the memory cell array 11, a single block BKincludes a plurality of (for example, two) areas FNG (FNG0 and FNG1).Each of the areas FNG includes one or more string units SU. For example,a single area FNG includes two string units SU.

Each of the NAND strings 111 includes a plurality of memory cells (alsoreferred to as memory portions or memory elements) MC and a plurality ofselect transistors ST1 and ST2.

Each of the memory cells MC (MC0, MC1, . . . , MC(m−2), and MC(m−1))includes a control gate and a charge storage layer. In the NAND string111, the plurality of memory cells MC are connected in series to eachother between the two select transistors ST1 and ST2. Among theplurality of memory cells MC connected in series to each other, one end(one of a source or a drain) of the memory cell MC on a drain side isconnected to one end of the drain side select transistor ST1. Among theplurality of memory cells MC connected in series to each other, one endof the memory cell MC on a source side is connected to one end of thesource side select transistor ST2.

A plurality of word lines WL (WL0, WL1, . . . , WL(m−2), and WL(m−1))are respectively connected to gates of the corresponding memory cellsMC. Here, “m” is a natural number of 2 or more. For example, a singleword lines WL is connected in common to the memory cells MC in aplurality of string units SU.

Data writing and data reading are collectively performed on the memorycells MC connected to any one of word lines WL in any one of stringunits SU. The unit of data reading and data writing is referred to as apage.

A plurality of drain side select gate lines SGD (SGD0 to SGD3) arerespectively connected to gates of the drain side select transistors ST1of the corresponding string units SU.

A plurality of source side select gate lines SGS (SGS0 and SGS1) areconnected in common to gates of the source side select transistors ST2of the string units SU. In the example illustrated in FIG. 3, two sourceside select gate lines SGS are provided in a single block BK. A singlesource side select gate line SGS is used in common for two string unitsSU in the area FNG. The two source side select gate lines SGS in twodifferent areas FNG are separated from each other.

A source line SL is connected to the other end (the other of the sourceand the drain) of the source side select transistor ST2. The other endof the drain side select transistor ST1 is connected to any one of aplurality of bit lines BL (BL0, BL1, . . . , and BL(n−1)). Here, “n” isa natural number of 1 or more.

In the flash memory of the present embodiment, the block BK includes aplurality of select gate lines SGM (SGM0 and SGM1). Consequently, eachof the NAND strings 111 includes one or more select transistors ST3.

One or more select gate lines SGM are provided in a single area FNG. Theselect gate line SGM is provided between two word lines WLi and WL(i−1).Here, “i” is a natural number of 0 or more and (m−1) or less.

For example, in the area FNG, the select gate line SGM is used in commonfor a plurality of string units SU. In the example illustrated in FIG.3, one select gate line SGM0 is connected to the string units SU0 andSU1, and the other select gate line SGM1 is connected to the stringunits SU2 and SU3. Consequently, the select gate lines SGM arecontrolled separately for each area FNG.

The select transistor ST3 is provided between two memory cells MC in theNAND string 111. One end of the select transistor ST3 is connected toone end of the memory cells MC adjacent to each other on the drain side.The other end of the select transistor ST3 is connected to one end ofthe memory cells MC adjacent to each other on the source side. A gate ofthe select transistor ST3 is connected to the select gate line SGM.

In the description given herein, the select gate lines SGM will bereferred to as intermediate select gate lines SGM. The selecttransistors ST3 connected to the intermediate select gate lines SGM willbe referred to as intermediate select transistors ST3.

As illustrated in FIG. 3, a plurality of memory cells MC are providedbetween the drain side select transistor ST1 and the intermediate selecttransistor ST3. A plurality of memory cells MC are provided between thesource side select transistor ST2 and the intermediate select transistorST3. The flash memory 1 of the present embodiment can control electricalconnection between the plurality of memory cells on the drain side andthe plurality of memory cells on the source side by using theintermediate select transistors ST3 and the intermediate select gatelines SGM.

A dummy word line may be provided in each string unit SU. The dummy wordline is configured with at least one word line provided near each ofselect gate lines SGD, SGS and SGM. In the flash memory of the presentembodiment, at least one of word lines WL adjacent to the select gatelines SGD, SGS and SGM, for example, at least one of word lines WL0,WL(i−1), WLi, and WL (m−1) may be used as the dummy word line. The dummyword line has an address which is not selected as a data writing target.Memory cells connected to the dummy word line are not used to hold datafrom a user.

The number of blocks BK in the memory cell array 11, the number ofstring units SU in a single block BK, or the number of memory cells MCin the NAND string 111 is not limited to any particular number.

Two or more intermediate select gate lines SGM may be provided in asingle string unit SU. In such a case, a plurality of intermediateselect transistors are provided in a single NAND string 111. A singleintermediate select gate line SGM may be provided separately for each ofa plurality of string units SU. In such a case, a single intermediateselect gate line SGM is provided in a single string unit SU.

The source side select gate lines SGS may be separately provided in therespective string units SU.

A selected string unit and a non-selected string unit are set in theblock by controlling a potential of the select gate line.

FIG. 4 is a schematic equivalent circuit diagram for explaining aninternal configuration of the row control circuit in the flash memory ofthe present embodiment.

As illustrated in FIG. 4, a single address decoder 120 and a singleswitch circuit 121 are provided for a single block BK.

The switch circuit 121 is connected to selection signal lines 90 and 90z of the address decoder. The switch circuit 121 can control enablingand disabling of the block BK based on signals (address decodingresults) DEC and bDEC from the address decoder 120. The signals DEC andbDEC have mutually complementary signal levels (an “H” level and an “L”level).

The switch circuit 121 includes a word line switch unit 291, a drainside select gate line switch unit 292, a source side select gate lineswitch unit 293, and an intermediate select gate line switch unit 294.Each of the switch units 291, 292, 293 and 294 includes a high breakdownvoltage transistor as a switch.

The word line switch unit 291 includes switches (selection switches) WSWof the same number as the number of word lines in the block BK. One endof a current path of each switch WSW is connected to a single word lineWL, and the other end of the current path of each switch WSW isconnected to a single CG line CG corresponding to the word line WL. Acontrol terminal (a gate of the transistor) of each switch WSW isconnected to the selection signal line 90 of the address decoder 120.Turning-on and turning-off of each switch WSW are controlled based onthe signal (block selection signal) DEC on the selection signal line 90.

A turned-on switch WSW allows various voltages corresponding tooperations of the flash memory to be transmitted to the word lines WL inthe selected block BK.

The drain side select gate line switch unit 292 includes a plurality ofswitches (selection switches) DSW0, DSW1, DSW2 and DSW3. The number ofswitches DSW0 to DSW3 is the same as the number of drain side selectgate lines SGD in the block. The switches DSW0 to DSW3 respectivelycorrespond to the drain side select gate lines SGD0 to SGD3 on aone-to-one basis.

One ends of the switches DSW0 to DSW3 are connected to the drain sideselect gate lines SGD0 to SGD3. The other ends of the switches DSW0 toDSW3 are respectively connected to wirings SGDI0 to SGDI3.

Control terminals of the respective the switches DSW0 to DSW3 areconnected to the selection signal line 90. Turning-on and turning-off ofthe switches DSW0 to DSW3 are controlled based on the signal DEC.

The drain side select gate line switch unit 292 includes a plurality ofswitches (non-selection switches) UDSW0, UDSW1, UDSW2 and UDSW3. Thenumber of switches UDSW is the same as the number of drain side selectgate lines SGD in the block BK. The switches UDSW0, UDSW1, UDSW2 andUDSW3 respectively correspond to the drain side select gate lines SGD0to SGD3 on a one-to-one basis.

One ends of the switches UDSW0, UDSW1, UDSW2 and UDSW3 are respectivelyconnected to the drain side select gate lines SGD0 to SGD3. The otherends of the switches UDSW0, UDSW1, UDSW2 and UDSW3 are connected incommon to a wiring USGDI. Control terminals of the switches UDSW areconnected to the selection signal line 90 z. Turning-on and turning-offof the switches UDSW are controlled based on the signal bDEC.

If the switches DSW are turned on due to the signal DEC having an “H”level, the switches UDSW are turned off due to the signal having an “L”level. In this case, the drain side select gate lines SGD arerespectively electrically connected to the wirings SGDI. The turned-onswitches DSW allow voltages applied to the respective wirings SGDIaccording to operations of the flash memory and selection addresses tobe transmitted to the drain side select gate lines SGD in a selectedblock.

If the switches UDSW are turned on due to the signal bDEC having an “H”level, the drain side select gate lines SGD are respectivelyelectrically connected to the wirings USGDI. The turned-on switches UDSWallow voltages of the wirings USGDI to be transmitted to the drain sideselect gate lines SGD in a non-selected block.

The source side select gate line switch unit 293 includes a plurality ofswitches (selection switches) SSW0 and SSW1. The number of switches SSW0and SSW1 is the same as the number of source side select gate lines SGSin the block BK. The switches SSW0 and SSW1 respectively correspond tothe source side select gate lines SGS0 and SGS1 on a one-to-one basis.

One ends of the switches SSW0 and SSW1 are respectively connected to thesource side select gate lines SGS0 and SGS1. The other ends of theswitches SSW0 and SSW1 are respectively connected to wirings SGSI0 andSGSI1.

Control terminals of the switches SSW0 and SSW1 are connected to theselection signal line 90 of the address decoder 120. Turning-on andturning-off of the switches SSW0 and SSW1 are controlled based on thesignal DEC.

The source side select gate line switch unit 293 includes a plurality ofswitches (non-selection switches) USSW0 and USSW1. The number ofswitches USSW0 and USSW1 is the same as the number (for example, two) ofsource side select gate lines SGS in the block BK. The switches USSWrespectively correspond to the source side select gate lines SGS on aone-to-one basis.

One ends of the switches USSW0 and USSW1 are respectively connected tothe source side select gate lines SGS0 and SGS1. The other ends of theswitches USSW0 and USSW1 are connected in common to wirings USGSI.

Control terminals of the switches USSW are connected to the selectionsignal line 90 z. Turning-on and turning-off of the switches USSW arecontrolled based on the signal bDEC.

If the switches SSW are turned on, and the switches USSW are turned off,based on the signals DEC and bDEC, the turned-on switches SSW allowvoltage applied to the wirings SGSI according to operations of the flashmemory and selection addresses to be transmitted to the source sideselect gate lines SGS. In contrast, if the switches SSW are turned off,and the switches USSW are turned on, the turned-on switches USSW allow avoltage applied to the wiring USGSI to be transmitted to the source sideselect gate lines SGS.

In the flash memory 1 of the present embodiment, the block BK includesthe intermediate select gate lines SGM. Switches (selection switches)MSW0 and MSW1 correspond to the intermediate select gate lines SGM0 andSGM1, and switches (non-selection switches) UMSW0 and UMSW1 respectivelycorrespond to the intermediate select gate lines SGM0 and SGM1.

The number of switches MSW and the number of switches UMSW are selectedaccording to the number of the intermediate select gate lines SGM in asingle block BK. As in the example illustrated in FIG. 3, if twointermediate select gate lines SGM are provided in a single block BK,the number of switches MSW is two, and the number of switches UMSW istwo.

One ends of the switches MSW0 and MSW1 are respectively connected to theintermediate select gate lines SGM0 and SGM1, and the other ends of theswitches MSW0 and MSW1 are respectively connected to wirings SGMI0 andSGMI1. Control terminals of the switches MSW are connected to theselection signal line 90. Turning-on and turning-off of the switches MSWare controlled based on the signal DEC.

One ends of the switches UMSW0 and UMSW1 are respectively connected tothe intermediate select gate lines SGM0 and SGM1, and the other ends ofthe switches UMSW0 and UMSW1 are connected to a wiring USGMI. Gates ofthe switches UMSW are connected to the selection signal line 90 z.Turning-on and turning-off of the switches UMSW are controlled based onthe signal bDEC.

If the switches MSW are turned on, and the switches UMSW are turned off,based on the signals DEC and bDEC, the turned-on switches MSW allowvoltage applied to the wirings SGMI according to operations of the flashmemory and selection addresses to be transmitted to the intermediateselect gate lines SGM. In contrast, if the switches MSW are turned off,and the switches UMSW are turned on, the turned-on switches UMSW allow avoltage applied to the wiring USGMI to be transmitted to theintermediate select gate lines SGM.

The number of switches in the switch circuit 121 is changed depending onthe number of word lines and select gate lines in the block BK.

Structure Example

With reference to FIGS. 5 to 7, a description will be given for astructure example of the flash memory of the present embodiment.

FIG. 5 is a perspective view schematically illustrating a structureexample of the memory cell array in the flash memory of the presentembodiment.

FIG. 5 illustrates an extracted single area FNG (two string units SU) ofthe two areas FNG in a single block.

As illustrated in FIG. 5, the flash memory of the present embodimentincludes the memory cell array 11 having a three-dimensional structure.A plurality of memory cells MC are arranged in a D1 direction and a D2direction which are parallel to a surface of a substrate 700, and arestacked in a D3 direction which is perpendicular to the surface of thesubstrate 700. The select gate lines SGD, SGS and SGM and the word linesWL are stacked in the D3 direction.

The word lines WL and the select gate lines SGD, SGS and SGM areconfigured with conductive layers 70, 71, 72 and 73. Insulating layers77 are provided between the stacked conductive layers 70, 71, 72 and 73.Consequently, in the stacked conductive layers 70, 71, 72 and 73, acertain conductive layer is electrically separated from an underlying oran overlying conductive layer.

Semiconductor pillars 75 are provided in the stacked select gate linesSGD (71), SGS (72) and SGM (73), and the word lines WL (70). Thesemiconductor pillars 75 are columnar semiconductor layers extending inthe D3 direction.

The memory cells MC and the select transistors ST1, ST2 and ST3 areprovided on side surfaces of the semiconductor pillars 75. More specificstructures of the memory cells MC and the select transistors ST1, ST2and ST3 will be described later.

The select gate lines SGD, SGS and SGM and the word lines WL areextracted in the D2 direction in a region 199 on one end side of thememory cell array 11. The region 199 in which the select gate lines SGD,SGS and SGM and the word lines WL are extracted will be referred to asan extraction region (or a hookup region). The extraction region 199 isprovided on one end side of the memory cell array 11.

A stacked structure including the wirings WL, SGD, SGS and SGM has astepped shape in the extraction region 199. Consequently, upper surfacesof the respective wirings are exposed at ends of the wirings WL, SGD,SGS and SGM in the extension direction (D2 direction), and thus regions(hereinafter, referred to as contact regions) in which contact plugs CPare disposed are secured on the upper surfaces of the respectivewirings.

The source side select gate lines SGS (conductive layers 72) areprovided under the stacked structure. The drain side select gate linesSGD (conductive layers 71) are provided on an upper side in the stackedstructure. The plurality of word lines WL are provided between the drainside select gate lines SGD and the source side select gate lines SGS inthe D3 direction.

In the present embodiment, the intermediate select gate lines SGM areprovided between the drain side select gate lines SGD and the sourceside select gate lines SGS in the D3 direction. The intermediate selectgate lines SGM are interposed between the word lines WL (or the dummyword lines) in the D3 direction.

The plurality of word lines WL (conductive layers 70) are divided intotwo groups with the intermediate select gate lines as boundaries. Aplurality of word lines WL between the intermediate select gate linesSGM and the source side select gate lines SGS are included in a firstgroup. A plurality of word lines WL between the intermediate select gatelines SGM and the drain side select gate lines SGD are included in asecond group.

FIG. 6 is a top view schematically illustrating a structure example ofthe memory cell array in the flash memory of the present embodiment.FIG. 6 illustrates layouts of the respective wirings in the extractionregion 199. FIG. 6 illustrates two areas FNG0 and FNG1 in the block BK.In FIG. 6, wirings (dashed lines in the figure) CG, SGDI, SGSI and SGMIfor applying voltages to a selected block are illustrated, wirings forapplying voltages to a non-selected block are not illustrated.

As illustrated in FIG. 6, plugs CPS (CPS0 and CPS1) are provided on thecontact region of the source side select gate lines SGS. The source sideselect gate lines SGS of the areas FNG0 and FNG1 are connected todifferent wirings SGSI as described above.

A plug CPW is provided on the contact region of each of the word linesWL.

The contact regions of the even-numbered word lines WL and the contactregions of the odd-numbered word lines WL are arranged in the D1direction above the source side select gate lines SGS. However,positions (heights from the surface of the substrate 700) of the contactregions of the even-numbered word lines WL in the D3 direction aredifferent from positions of the contact regions of the odd-numbered wordlines in the D3 direction.

As mentioned above, with respect to two stacked wirings, two contactregions are adjacent to each other in the D1 direction intersecting theD2 direction, and thus a size of the extraction region in the D2direction is reduced.

Regarding the respective word lines WL, even if the word lines areincluded in different areas FNG, the word lines (word lines having thesame wiring level) WL having the same address number are connected tothe common wiring CG.

Plugs CPM (CPM0 and CPM1) are provided in the contact regions of theintermediate select gate lines SGM. In the areas FNG0 and FNG1, theintermediate select gate lines SGM are connected to different wiringsSGMI via the plugs CPM.

Also regarding the word lines WL(i) to WL(m−1) above the intermediateselect gate lines SGM, plugs CPW are provided on the contact regions ofthe word lines WL in the same layouts as those of the word lines WLbelow the intermediate select gate lines SGM.

The drain side select gate lines SGD are provided above the intermediateselect gate lines SGM and the word lines WL.

The drain side select gate lines SGD are separated for each of thestring units SU. If a single block BK includes four string units SU, twodrain side select gate lines SGM are provided in each area FNG. PlugsCPD are provided on the contact regions of the respective drain sideselect gate lines SGD. The drain side select gate lines SGM0 to SGM3 arerespectively connected to different wirings SGMI0 SGMI3 via the plugsCPD.

For example, dummy wirings (dummy word lines) may be provided in thememory cell array. The dummy word lines are adjacent to the select gatelines SGD, SGS and SGM in the D3 direction. Contact regions of the dummyword lines have the same layout as the layout of the contact regions ofthe word lines WL. The respective dummy word lines are connected to thecommon wiring CG in a plurality of areas FNG and a plurality of stringunits SU in the same manner as in the connection relationship betweenthe word lines WL and the wiring CG. However, in dummy word linesadjacent to the intermediate select gate lines SGM, potentials of thedummy word lines may be controlled in the same manner as in control ofpotentials of the intermediate select gate lines SGM. In this case, thedummy word lines are connected to wirings in a relationship similar tothe connection relationship between the intermediate select gate linesSGM and the wirings SGMI.

Bit line contacts BC are provided on the semiconductor pillars 75. Thebit line contacts BC are connected to bit lines BL.

Two NAND strings 111 adjacent to each other in the D1 direction areconnected to different bit lines BL. In this case, two bit line contactsBC adjacent to each other are not arranged on the same straight linewhich is parallel to the D1 direction in a D1-D2 plane. In a pluralityof NAND strings 111 arranged in the D1 direction, positions of the bitline contacts BC are alternately deviated in the D2 direction. Aplurality of NAND strings 111 arranged in an inclined direction areconnected to different bit lines BL.

FIG. 7 is a schematic sectional view for explaining the entireconfiguration of the block in the memory cell array of the flash memoryof the present embodiment.

As illustrated in FIG. 7, in the memory cell array 11, the block BK isprovided on a p-type well region 702 inside the semiconductor substrate(for example, a Si substrate or a semiconductor layer on an insulatinglayer) 700.

For example, the NAND string 111 in the block BK is provided in a regionsurrounded by well contacts CPW. The well contacts CPW are provided onp⁺-type diffusion layers 703 in the p-type well region 702. A sourceline contact CELSRC is provided on an n⁺-type diffusion layer 704 in thep-type well region 702 between the two areas FNG. The source linecontact CELSRC is connected to the source line SL. Each of the contactCPW and CELSRC has a structure in which two plugs are stacked in the D3direction.

In the flash memory 1 of the present embodiment, the block BK includes aplurality of array layers (memory stages) 110A and 110B. In FIG. 7, ineach area FNG, two array layers 110A and 110B are stacked in the D3direction. The array layer 110A (hereinafter, referred to as a lowerarray layer) on the lower side includes a plurality of semiconductorpillars (hereinafter, referred to as lower semiconductor pillars) 75A.The array layer 110B (hereinafter, referred to as an upper array layer)on the upper side includes a plurality of semiconductor pillars(hereinafter, referred to as upper semiconductor pillars) 75B. Thesemiconductor pillars 75A and 75B extend substantially in a verticaldirection (D3 direction) with respect to the surface of the p-type wellregion 702 (substrate). The semiconductor pillars 75A and 75B arearranged in an array form in the respective array layers 110A and 110Balong the D1 direction and the D2 direction.

Each of the NAND strings 111 is provided on the p-type well region 702so as to encompass the two array layers 110A and 110B. The NAND string111 includes two semiconductor pillars 75A and 75B. The lowersemiconductor pillar 75A is provided on the upper semiconductor pillar75B. A lower end of the semiconductor pillar 75A is connected to thep-type well region 702. An upper end of the semiconductor pillar 75A isconnected to a lower end of the semiconductor pillar 75B. The bit lineBL are provided above the upper ends of the semiconductor pillars 75Bvia the bit line contacts BC.

A plurality of conductive layers 70, 71, 72 and 73 are stacked on thep-type well region 702. The respective conductive layers 70, 71, 72 and73 oppose side surfaces of the semiconductor pillars 75 via memory films(not illustrated).

A drain side select transistor STD is disposed in a region including theupper semiconductor pillar 75B and one or more conductive layers 71. Forexample, a plurality of (for example, three) stacked conductive layers71 serve as a gate electrode of the select transistor STD. The pluralityof stacked conductive layers 71 function as the drain side select gatelines SGD.

In the area FNG, the conductive layers 71 are provided in each of thestring units SU. Consequently, potentials of the drain side select gatelines SGD are separately controlled in the two string units SU in thearea FNG.

A source side select transistor STS is disposed in a region includingthe lower semiconductor pillar 75A and one or more conductive layers 72.The conductive layers 72 serve as a gate electrode of the source sideselect transistor STS. The conductive layers 72 function as the sourceside select gate lines SGS.

For example, in a single area FNG, the conductive layer 72 as the sourceside select gate line SGS is used in common to two string units SU.Consequently, a potential of the source side select gate line SGS iscontrolled in common in two string units SU in the area FNG.

The memory cells MC are disposed in a region including the semiconductorpillars 75A and 75B and the conductive layers 70. The conductive layers70 serve as control gate electrodes of the memory cells MC. A singleconductive layer 70 functions as a single word line WL. In the area FNG,the conductive layers 70 as the word lines WL are used in common to twostring units SU. The conductive layers 70 may be used in common to fourstring units SU in the two areas FNG.

The intermediate select gate line SGM and the intermediate selecttransistor ST3 are provided in a region near a boundary (hereinafter, aboundary region) 799 between the two array layers 110A and 110B. Forexample, the boundary region 799 includes at least a first conductivelayer of the lower array layer 110A and a first conductive layer of theupper array layer 110B when counted from a junction between the twosemiconductor pillars 75A and 75B. In the example illustrated in FIG. 7,the boundary region 799 includes three conductive layers of the lowerarray layer 110A and three conductive layers of the upper array layer110B centering on the junction between the two semiconductor pillars 75Aand 75B.

In the example illustrated in FIG. 7, a plurality of intermediate selectgate lines SGM are provided in the string unit SU. The conductive layer73 of the upper array layer 110B and the conductive layer 73 of thelower array layer 110A are provided as the intermediate select gatelines SGM. In each area FNG, the conductive layers 73 are used in commonto two string units SU.

The intermediate select transistor ST3 is disposed in a region includingthe semiconductor pillars 75A and 75B, and the conductive layers 73. Theconductive layers 73 function as the intermediate select gate lines SGM,and also function as a gate electrode of the intermediate selecttransistor ST3.

FIG. 8 is a schematic sectional view for explaining a structure exampleof the NAND string. FIG. 8 illustrates an extracted single NAND string.

As illustrated in FIG. 8, in the NAND string 111, the memory cells MCinclude memory films 79 (79A and 79B) between the semiconductor pillars75 and the conductive layers (word lines) 70. The memory films 79 coverthe side surfaces of the semiconductor pillars 75.

The memory film 79A is continued on the side surface of thesemiconductor pillar 75A from the upper end of the semiconductor pillar75A to the lower end thereof. The memory film 79B is continued on theside surface of the semiconductor pillar 75B from the upper end of thesemiconductor pillar 75B to the lower end thereof. The memory film 79Ais separated from the memory film 79B.

The memory films 79 have a stacked structure. Each of the memory films79 includes a gate insulating film 791, a charge storage layer 792, anda block insulating film 793.

The gate insulating film (tunnel insulating film) 791 is provided on theside surface of the semiconductor pillar 75. The charge storage layer792 is provided between the gate insulating film 791 and the blockinsulating film 793. The charge storage layer 792 includes an insulatingfilm (for example, a SiN film) having a trap level. The charge storagelayer 792 may include a semiconductor film (for example, a siliconfilm). If the charge storage layer 792 includes the semiconductor film,the semiconductor film is separately formed for each memory cell MC. Theblock insulating film 793 is provided between the charge storage layer792 and the conductive layer 70.

The memory film 79 is also provided between the gate electrodes (theconductive layers 71, 72 and 73) of the select transistors ST1, ST2 andST3, and the semiconductor pillar 75.

The semiconductor pillars 75A and 75B serve as channel regions of thememory cells MC. The semiconductor pillars 75A and 75B contain amorphoussilicon or polysilicon. For example, the semiconductor pillar 75 mayinclude a columnar insulator (for example, silicon oxide) and asemiconductor region 751 covering a side surface of the columnarinsulator.

For example, as illustrated in FIG. 8, the semiconductor pillars 75A and75B may have a tapered sectional shape upon manufacturing of the memorycell array. In this case, a dimension (diameter) of the lower part ofthe semiconductor pillar 75 in the D2 direction (and the D1 direction)is smaller than a dimension of the upper part of the semiconductorpillar 75 in the D2 direction.

As in the example illustrated in FIG. 8, the conductive layer (at leastone of the lowermost conductive layer of the upper array layer and theuppermost conductive layer of the lower array layer) adjacent to thejunction 999 may be used as a dummy word line DWL. In this case, aconductive layer directly on the dummy word line DWL or a conductivelayer directly under the dummy word line DWL is used as the intermediateselect gate line SGM.

FIG. 9 is a diagram for explaining a relationship between thresholdvoltage of the memory cell and data which can be stored. As illustratedin FIG. 9, if the memory cell MC stores data of 2 bits (“11”, “10”,“01”, and “00”), a threshold voltage of a plurality of memory cells MCin the memory cell array (a block or a page) may have four thresholdvoltage value distributions (states or levels) TD-Er, TD-A, TD-B, andTD-C so as to correspond to 2-bit (four-valued) data.

The Er level corresponds to an erasing state. The A level, the B level,and the C level correspond to a data storing state (holding state). Whendata is stored, a threshold voltage of the memory cell MC is included inany one of threshold voltage value distributions TD-A, TD-B and TD-C ofthe A level, the B level, and the C level. Consequently, the memory cellMC stores 2-bit data.

Determination levels (determination voltages) VA, VB, and VC for readingdata are set among the threshold voltage value distributions.Consequently, when data is read from the memory cell MC, data held inthe memory cell MC is determined. For example, if the memory cell stores2-bit data, the levels VA, VB, and VC are used as determination levels(hereinafter, also referred to as reading levels) for reading data.

A reading pass voltage VREAD has a voltage value higher than an upperlimit voltage value of the highest threshold voltage value distribution(here, the C level) among the plurality of threshold voltage valuedistributions which can be taken by the memory cell MC. The memory cellMC to which the reading pass voltage VREAD is applied is turned onregardless of stored data.

Determination levels (hereinafter, also referred to as verificationlevels) for verifying writing of data are set around lower limit voltagevalues of the respective threshold voltage value distributions.Consequently, when data is written into the memory cell MC, whether ornot the memory cell MC reaches a threshold voltage value distributioncorresponding to data to be written is determined. Levels VAV, VBV andVCV are respectively set in the threshold voltage value distributionsTD-A, TD-B and TD-C as the verification levels. Other levels fordetermining states of threshold voltages of the memory cell may beprovided between the reading levels and the verification levels as theverification levels.

During a read operation of the flash memory 1, a reading voltage havingat least one of the plurality of reading levels is applied to the memorycell. During an operation of verifying a write operation of the flashmemory 1, a verification voltage having at least one of the plurality ofverification levels is applied to the memory cell. Consequently,determines whether or not the memory cell MC is turned on is detected inthe read operation and the verification operation. As a result, a stateof data stored in the memory cell or a threshold voltage of the memorycell during writing of data is determined.

Data stored in the memory cell MC is not limited to 2-bit data, and asingle memory cell MC may store 1-bit data. A single memory cell MC maystore data of 3 or more bits.

In the present embodiment, the structure, operation, and manufacturingmethod of the memory cell array having the three-dimensional structureare as disclosed in, for example, U.S. patent application Ser. No.12/407,403, filed on Mar. 19, 2009, entitled “three-dimensional stackednonvolatile semiconductor memory,” U.S. patent application Ser. No.12/406,524, filed on Mar. 18, 2009, entitled “three-dimensional stackednonvolatile semiconductor memory,” U.S. patent application Ser. No.12/679,991, filed on Mar. 25, 2010, entitled “nonvolatile semiconductormemory device and manufacturing method thereof,” and U.S. patentapplication Ser. No. 12/532,030, filed on Mar. 23, 2009, entitled“semiconductor memory and manufacturing method thereof.” All of thesepatent applications are incorporated by reference herein.

FIGS. 10A and 10B are diagrams for explaining the flash memory of thepresent embodiment. FIGS. 10A and 10B are diagrams schematicallyillustrating an operation of the flash memory of the present embodiment.In FIGS. 10A and 10B, for clarity in illustration, the bit lines and thesource lines are not illustrated. In the following description, areference sign of a drain side select gate line (selected drain sideselect gate line) of a selected string unit including selected cellsbased on selection addresses uses “SGD-S”, and a reference sign of asource side select gate line (selected source side select gate line) ofa selected string unit including selected cells based on selectionaddresses uses “SGS-S”. A reference sign of a drain side select gateline (non-selected drain side select gate line) of a non-selected stringunit including selected cells based on selection addresses uses“SGD-US”, and a reference sign of a source side select gate line(non-selected source side select gate line) of a non-selected stringunit including selected cells based on selection addresses uses“SGS-US”.

Regarding the intermediate select gate line SGM, a reference sign of aselected intermediate select gate line uses “SGM-S”, and a referencesign of a non-selected intermediate select gate line uses “SGM-US”.

A reference sign of a selected word line uses “WL-S”, and a referencesign of a non-selected word line uses “WL-US”.

As described above, the flash memory of the present embodiment includesthe intermediate select gate lines SGM and the intermediate selecttransistors ST3 in the NAND string 111. Consequently, the flash memoryof the present embodiment can electrically separate at least apart ofone of the lower array layer 110A and the upper array layer 110B fromthe bit line BL and the source line SL (CELSRC) according to anoperation of the memory.

During a read operation (or a verification operation) of the flashmemory, electric charge (hereinafter, referred to as residual electriccharge) remaining in the semiconductor pillar may be injected into thecharge storage layer due to a voltage being applied to the word line.Thus, there is a probability that reading disturbance may occur in thememory cell.

In order to reduce reading disturbance, a process (hereinafter, referredto as a release process) of releasing the residual electric charge inthe semiconductor pillar may be performed as an initial operation of theread operation.

In the release process, the semiconductor pillar is electricallyconnected to at least one of the bit line and the source line.Consequently, the residual electric charge is released from thesemiconductor pillar to the bit line or from the semiconductor pillar tothe source line.

If the semiconductor pillar is electrically connected to the bit line orthe source line during the release process, a capacitance component(parasitic capacitance) is generated in a NAND string of a non-selectedstring unit due to a potential difference between the word line and thesemiconductor pillar when a threshold voltage of the memory cell isdetermined after the release process. The capacitance component acts asa load during a read operation. Thus, this load may cause an increase ina current (power consumption), the occurrence of noise, deterioration inan operation speed, and the like during a read operation (or averification operation) of the flash memory.

If a block includes a plurality of array layers in order to increase amemory capacity, the number of memory cells, the number of word lines,and the number of wirings used in common to a plurality of elements in ablock are increased, and thus the influence of a load due to acapacitance component further increases.

The flash memory of the present embodiment electrically separates anupper array layer and a lower array layer in a non-selected string unitfrom each other by controlling a potential of the intermediate selectgate line SGM during a read operation (or a verification operation).Consequently, the flash memory of the present embodiment performs arelease process on residual electric charge in the semiconductor pillarin a memory stage including a selected word line in a non-selectedstring unit.

Along with the electric charge release process, in the flash memory ofthe present embodiment, in the non-selected string unit SU, an arraylayer not including the selected word line is electrically separatedfrom the bit line and the source line by turning off the selecttransistor ST3. As a result, the flash memory of the present embodimentcan perform channel-boosting on the semiconductor pillar in an arraylayer not including a selected word line in a non-selected string unit.

FIG. 10A is a diagram schematically illustrating a conduction statebetween respective members in a block if there is a selected word linein the upper array layer 110B. FIG. 10A illustrates a relationshipbetween potentials during a release process before data is read.

In FIG. 10A, the drain side select gate line SGD0 corresponds to aselected drain side select gate line SGD-S based on a selection address,and the source side select gate line SGS0 corresponds to a selectedsource side select gate line SGS-S based on a selection address.

In FIG. 10A, a voltage having an “H” level (transistor turning-onvoltage) is applied to the respective select gate lines SGD-S, SGS-S andSGM-S of the selected string unit SU0. Consequently, in the selectedstring unit, the semiconductor pillars of each NAND string areelectrically connected to the bit line and the source line.

When a threshold voltage of the memory cell is determined after arelease process during a read operation or a verification operation, anon-selected string unit is a string unit in which at least a drain sideselect gate line is disabled among a plurality of select gate lines in astring unit. In the non-selected string unit, a turning-off voltage ofthe select transistor ST1 is applied to the drain side select gate lineSGD during a determination of a threshold voltage of the memory cell.Consequently, the non-selected string unit is electrically separatedfrom the bit line BL.

In the case of FIG. 10A, a voltage having an “H” level is applied to thedrain side select gate lines SGD-US in the non-selected string unitsSU1, SU2 and SU3.

If a voltage having an “L” level (transistor turning-off voltage) isapplied to the intermediate select gate lines SGM-US of the non-selectedstring units, the lower semiconductor pillar 75A of the lower arraylayer 110A is electrically separated from the bit line BL, the sourceline SL (CELSRC), and the upper semiconductor pillar 75B of the upperarray layer 110B.

However, as illustrated in FIG. 10A, if a select gate line is shared bythe string units SU0 and SU1 adjacent to each other as in the sourceside select gate line SGS and the intermediate select gate line SGM,potentials of the shared select gate lines SGS and SGM are the same aseach other in the non-selected string unit SU1 and the selected stringunit SU0. Therefore, in the non-selected string unit SU1, the selecttransistors ST2 and ST3 are turned on, and thus the lower semiconductorpillar 75A is electrically connected to the upper semiconductor pillar75B and the source line SL (CELSRC).

In this case, an electric charge release process is performed on thesemiconductor pillar 75B in the upper array layer 110B including theselected word line WL-S in the non-selected string unit along with thesemiconductor pillars 75A and 75B of the selected string unit. As aresult, the flash memory of the present embodiment can reduce readingdisturbance caused by hot electrons.

During a determination of a threshold voltage of the memory cell, thereading pass voltage VREAD is applied to the word line WL, and thus thesemiconductor pillar 75A in a portion 99A of the lower array layer 110Ais subject to channel boosting. Consequently, a capacitance componentbetween the word line WL and the semiconductor pillar 75A is notgenerated in the lower array layer 110A of the non-selected string unit.As a result, the flash memory 1 of the present embodiment can reduce aload caused by a capacitance component.

FIG. 10B is a diagram schematically illustrating a conduction statebetween respective members in a block if there is a selected word linein the lower array layer 110A. FIG. 10B illustrates a relationshipbetween potentials during a release process before data is read.

In FIG. 10B, in the same manner as in the example illustrated in FIG.10A, the drain side select gate line SGD0 and the source side selectgate line SGS0 respectively correspond to selected select gate linesSGD-S and SGS-S.

In FIG. 10B, a voltage having an “H” level is applied to the respectiveselect gate lines SGD-S, SGS-S and SGM-S of the selected string unit. Ina non-selected string unit, a voltage having an “H” level is applied tothe non-selected source side select gate line SGS-US, and a voltagehaving an “L” level is applied to the non-selected drain side selectgate line SGD-US. A voltage having an “L” level is applied to theintermediate select gate line SGM of the non-selected string unit.Consequently, in the non-selected string unit, the intermediate selecttransistors ST3 are turned off, and thus the upper semiconductor pillar75B is electrically separated from the bit line BL, the lowersemiconductor pillar 75A, and the source line SL.

As illustrated in FIG. 10B, in the non-selected string unit SU1 whichshares the select gate lines SGS and SGM with the selected string unitSU0, the select transistors ST2 and ST3 of the non-selected string unitSU1 are turned on, and thus the semiconductor pillars 75A and 75B areconnected to the source line SL (CELSRC).

In this case, an electric charge release process is performed on thelower semiconductor pillar 75A in the lower array layer 110A includingthe selected word line in the non-selected string unit along with thesemiconductor pillars 75A and 75B of the selected string unit. As aresult, the flash memory of the present embodiment can reduce readingdisturbance caused by hot electrons.

During a determination of a threshold voltage of the memory cell, thereading pass voltage VREAD is applied to the word line WL, and thus thesemiconductor pillar 75B in a portion 99B of the upper array layer 110Bis subject to channel boosting. As a result, the flash memory 1 of thepresent embodiment can reduce a capacitance component between the wordline WL and the semiconductor pillar 75B in the non-selected stringunit, and can thus reduce a load during a read operation.

As mentioned above, the flash memory of the present embodiment canreduce reading disturbance while reducing the influence of a parasiticcapacitance.

Therefore, the flash memory of the present embodiment can improveoperation characteristics.

(1b) Operation Examples

With reference to FIGS. 11 to 16, a description will be made of anoperation example (control method) of a memory device according to afirst embodiment. Here, an operation of the memory device of the presentembodiment will be described with reference to FIGS. 1 to 10B asappropriate in addition to FIGS. 11 to 16.

(1b-1) Basic Example

With reference to FIG. 11, a description will be made for a basicexample of an operation of the memory device (for example, a flashmemory) of the present embodiment.

In the memory system including the flash memory of the presentembodiment, the memory controller 5 transmits commands and addresses(selection addresses) of operation targets to the flash memory 1 (stepS0).

The flash memory 1 receives the commands and the selection addresses.Consequently, the flash memory 1 starts an operation based on thecommands (step S1). The operation performed by the flash memory includesa determination of a threshold voltage of the memory cell. For example,the determination of a threshold voltage of the memory cell is includedin a read operation, or a verification operation in a write operation.

The flash memory 1 selects and enables a block, a string unit, and apage including operation target memory cells.

The flash memory 1 starts control on select gate lines in the selectedblock (step S2). Consequently, the drain side select gate line SGD, thesource side select gate line SGS, and the intermediate select gate linesSGM in the selected string unit SU are enabled. For example, in theselected string unit, a voltage VSG for turning on the selecttransistors ST1, ST2 and ST3 are applied to the selected select gatelines SGD, SGS and SGM.

In the present embodiment, the flash memory 1 disables the intermediateselect gate lines SGM with respect to non-selected string units. Theflash memory 1 of the present embodiment enables select gate lines inthe array layers 110A and 110B including selected word lines WL of thedrain side and source side select gate lines SGD and SGS, and disablesselect gate lines SGD and SGS in the array layers 110A and 110B notincluding the selected word lines WL.

As illustrated in FIG. 10A, if the word lines WL in the upper arraylayer 110B are selected as operation target addresses, the non-selecteddrain side select gate line SGD is enabled, and the non-selected sourceside select gate line SGS is disabled. The non-selected intermediateselect gate line SGM is disabled. For example, the voltage VSG isapplied to the non-selected drain side select gate line SGD, and avoltage (for example, a ground voltage) VSS for turning off the selecttransistor ST2 is applied to the non-selected source side select gateline SGS.

As illustrated in FIG. 10B, if the word lines WL in the lower arraylayer 110A are selected as operation target addresses, the non-selecteddrain side select gate line SGD is disabled, and the non-selected sourceside select gate line SGS is enabled. The non-selected intermediateselect gate line SGM is disabled. For example, the ground voltage VSSfor turning off the select transistor ST1 is applied to the non-selecteddrain side select gate line SGD, and the voltage VSG is applied to thenon-selected source side select gate line SGS.

The flash memory 1 controls enabling and disabling of the intermediateselect gate lines SGM of each string unit SU and then applies voltagesfor operating the memory cells to the word lines (step S3).

Consequently, in either one of the lower array layer 110A and the upperarray layer 110B in the non-selected string unit, residual electriccharge in the semiconductor pillars 75A and 75B is released to the bitline BL or the source line SL via the turned-on memory cell MC and theselect transistors. The release process is not performed on thesemiconductor pillar which is electrically separated from the bit lineBL and the source line SL by turning off the select transistor.

The flash memory 1 determines a threshold voltage of the memory cellconnected to the selected word line after performing the electric chargerelease process (step S4). If a determination of the threshold voltageof the memory cell MC is performed for a read operation, a readingvoltage is applied to the selected word line WL.

If a determination of the threshold voltage of the memory cell MC isperformed for a verification operation in a write operation, averification voltage is applied to the selected word line. During theread operation or the verification operation, the reading pass voltageVREAD is applied to word lines (non-selected word lines) other than theselected word line.

Data (a state of a threshold voltage of the memory cell) held in thememory cell is determined based on a turned-on or turned-off result ofthe memory cell when the reading voltage (or the verification voltage)is applied.

In the present embodiment, in the lower and upper array layers 110A and110B of the non-selected string unit, the semiconductor pillar in aportion which is electrically separated from other members by thedisabled select gate lines SGD, SGS and SGM is in an electricallyfloating state. Therefore, as in the portion 99A in FIG. 10A or theportion 99B in FIG. 10B, the semiconductor pillar 75 in the electricallyseparated array layer 110 is subject to channel boosting due to thereading pass voltage VREAD being applied to the non-selected word line,and thus a potential of the semiconductor pillar 75 increases.Consequently, a capacitance component in the portion 99 is reduced.

As a result, a load caused by a capacitance component of a non-selectedstring unit in a selected block is reduced during an operation of theflash memory.

If an operation including the above-described determination of athreshold voltage of the memory cell is performed one or more times, andthen the flash memory 1 detects finishing of an operation based on acommand, the flash memory 1 notifies the memory controller 5 offinishing of the operation (step S5). If the operation based on acommand is a read operation, the flash memory 1 transmits data to thememory controller 5.

The memory controller 5 is notified of the finishing of the operation bythe flash memory 1, and thus detects the finishing of the operation ofthe flash memory (step S6). If data is transmitted from the flash memory1 to the memory controller 5, the memory controller 5 receives the data,and transmits the received data to the host device.

Through the above-described operation, the read operation of the flashmemory of the present embodiment is completed.

As described above, during an operation of the flash memory, a loadcaused by a capacitance component between the word line and thesemiconductor pillar is reduced.

As a result, the flash memory of the present embodiment can improveoperation characteristics.

(b-2) Specific Example

With reference to FIGS. 12 to 16, a specific example of an operation ofthe flash memory of the present embodiment will be explained.

(b-2-1) Read Operation

With reference to FIGS. 12 and 13, a read operation of the flash memoryof the present embodiment will be explained.

FIGS. 12 and 13 are diagrams illustrating voltage waveforms of therespective wirings during a read operation of the flash memory of thepresent embodiment.

In the present embodiment, a current sensing method is used as a methodof controlling the bit line during the read operation (a process ofdetermining a threshold voltage of the memory cell). In the currentsensing method, a state of a threshold voltage of the memory cell isdetermined by sensing the generation of a bit line current (cellcurrent) according to turning-on or turning-off of the memory cell.

In the present embodiment, a spike operation is employed as a method ofcontrolling the word line during the read operation. In the spikeoperation, a voltage higher than a reading voltage is applied to a wordline (selected word line) indicated by an address and other word lines(non-selected word line), and then a potential of the selected word lineis read to be set as a voltage. The spike operation can allow electriccharge in the semiconductor pillar to be efficiently released.

Read Operation on Memory Cell of Upper Array Layer

With reference to FIG. 12, a data read operation on the memory cell ofthe upper array layer will be explained.

Time Point t0

For example, at a time point t0, the memory controller 5 transmits areading command CMD and a selection address ADR of a data reading targetto the flash memory 1 in response to a request from the host device 600.

The flash memory 1 receives the reading command CMD and the selectionaddress ADR. The sequencer 19 starts a read operation based on thereading command CMD.

The sequencer 19 controls each circuit of the flash memory 1 so that theread operation is performed as follows.

At the time point t0, the sequencer 19 causes a signal level of theready/busy signal R/B to transition from an “H” level to an “L” level.Consequently, the memory controller 5 is notified of starting of theread operation of the flash memory 1.

The voltage generation circuit 18 generates various voltages used forthe read operation under the control of the sequencer 19.

Time Point T1 a

At a time point t1 a, the source line driver 15 applies the groundvoltage VSS to the source line SL (CELSRC).

The row control circuit 12 applies the voltage VSG to a selected drainside select gate line SGD-S and a selected source side select gate lineSGS-S with respect to a selected string unit SU in a selected block BK.Consequently, the select transistors ST1 and ST2 are turned on.

The bit line BL is electrically connected to the semiconductor pillar 75via the turned-on select transistor ST1. The source line SL (CELSRC) iselectrically connected to the semiconductor pillar 75 via the turned-onselect transistor ST2 and the well region 702.

The row control circuit 12 applies the voltage VSG to non-selected drainside select gate lines SGD-US in non-selected string units SU in theselected block BK. The row control circuit 12 applies the ground voltageVSS to non-selected source side select gate lines SGS-US. Consequently,in the non-selected string units, the select transistors ST1 are turnedon, and the select transistors ST2 are turned off.

In the present embodiment, in the selected string unit (for example, thestring unit SU0) of the selected block BK, the row control circuit 12applies the voltage VSG from the driver 129 to the selected intermediateselect gate lines SGM-S. Consequently, the intermediate selecttransistors ST3 are turned on in the selected string unit SU.

In the non-selected string units of the selected block BK, the rowcontrol circuit 12 applies the ground voltage VSS to the non-selectedintermediate select gate lines SGM-US. Consequently, in the non-selectedstring units, the intermediate select transistors ST3 are turned off. Asa result, in the non-selected string unit, the semiconductor pillar 75Aof the lower array layer 110A is electrically separated from thesemiconductor pillar 75B of the upper array layer 110B by turning offthe intermediate select transistors ST3.

If word lines adjacent to the intermediate select gate lines SGM areused as dummy word lines in the respective string units, respectivepotentials of the dummy word lines are controlled to be the same aspotentials of the adjacent intermediate select gate lines SGM-S andSGM-US.

A time lag occurs from starting of application of a certain voltage to awiring until a potential of the wiring reaches the voltage due to wiringdelay.

Time Point t2 a

At a time point t2 a, the row control circuit 12 starts to apply thereading pass voltage VREAD to the non-selected word lines WL-US. The rowcontrol circuit 12 also starts to apply the reading pass voltage VREADto the selected word lines WL-S along with the application of thereading pass voltage VREAD to the non-selected word lines WL-US.Potentials of the non-selected word lines WL-US and the selected wordlines WL-S increase.

Consequently, during control of potentials of the non-selected wordlines WL-US, channels can be formed in memory cells (non-selected cells)connected to the non-selected word lines WL-US, and channels can also beformed in memory cells (selected cells) connected to the selected wordlines WL-S.

Electric charge in the semiconductor pillars 75 is released to the bitline BL or the source line SL via the formed channels.

As a result, local electric field concentration around a selected cellcan be prevented, and thus the occurrence of erroneous writing on theselected cell and a non-selected cell adjacent to the selected cell canbe reduced.

As mentioned above, in the present embodiment, the spike operation onthe word lines WL is performed.

Time Point t3 a

At a time point t3 a, in the sense amplifier circuit 13, the senseamplifier units 131 start to charge the respective bit lines BL underthe control of the sequencer 19.

A potential of the selected word line WL-S increases to a readingvoltage VCGRV or higher. The row control circuit 12 reduces thepotential of the selected word line WL-S to converge on the readingvoltage VCGRV. The reading pass voltage VREAD is continuously applied tothe non-selected word lines WL-US.

In the non-selected string units, the row control circuit 12 stopsapplication of the voltage to the drain side select gate lines SGD-US.Consequently, potentials of the non-selected drain side select gatelines SGD-US are set to the ground voltage VSS.

In the selected string unit, a potential of the drain side select gateline SGD-S, a potential of the source side select gate line SGS-S, andpotentials of the intermediate select gate lines SGM-S are maintained tobe the voltage VSG.

In the non-selected string units, potentials of the non-selectedintermediate select gate lines SGM-US are maintained to be the groundvoltage VSS.

In a period TA from the time point t1 a to the time point t3 a, thevoltage VSG is applied to the non-selected drain side select gate linesSGD-US, and thus the select transistors ST1 connected to thenon-selected drain side select gate lines SGD-US are turned on. In theperiod TA, the upper semiconductor pillars 75B of the non-selectedstring units are electrically connected to the bit lines BL. Electriccharge in the upper semiconductor pillars 75B is released to the bitlines BL via the turned-on select transistors ST1.

On the other hand, in the period TA, the ground voltage VSS is appliedto the non-selected intermediate select gate lines SGM-US and thenon-selected source side select gate lines SGS-US. Thus, the selecttransistors ST3 connected to the non-selected intermediate select gatelines SGM-US are turned off, and the select transistors ST2 connected tothe non-selected source side select gate lines SGS-US are turned off.

Therefore, the lower semiconductor pillars 75A of the non-selectedstring units are electrically separated from the bit lines BL and thesource line SL (CELSRC) and are thus in an electrically floating state.As a result, the semiconductor pillars 75A in a floating state aresubject to channel boosting due to increases in potentials of thenon-selected word lines WL-US.

Time Point t4 a

After a charging waiting period (development period) TB for the bit lineBL elapses, at a time point t4 a, a potential of the bit line BL issubstantially set to a voltage Vpre with a predetermined magnitude. Apotential of the selected word line WL-S is set to the reading voltageVCGRV, and a potential of the non-selected word line WL-US is set to thereading pass voltage VREAD.

The non-selected cell to which the reading pass voltage VREAD is appliedis turned on.

Regarding the selected cell MC, the memory cell MC having a thresholdvoltage which is equal to or lower than the reading voltage VCGRV isturned on, and the memory cell MC having a threshold voltage which ishigher than the reading voltage VCGRV is turned off.

If the selected cell MC is turned on due to the application of thereading voltage VCGRV, a current (cell current) flows between the bitline BL and the source line SL (CELSRC). A potential of a node connectedto the bit line BL in the sense amplifier unit 131 changes due to theoccurrence of the current. On the other hand, if the selected cell isturned off when the reading voltage VCGRV is applied, a current does notflow between the bit line BL and the source line SL connected to theturned-off selected cell. In this case, a potential of a node connectedto the bit line BL does not change.

The sense amplifier unit 131 senses the generation of a current in thebit line. The sense amplifier unit 131 incorporates a signalcorresponding to a result of the sensing into a latch circuitcorresponding to each bit line.

In the above-described way, regarding 1-bit data, whether data stored inthe memory cell MC is data of “1” or data of “0” is determined by usingthe reading voltage VCGRV as a reference (determination level).

In a determination of a threshold voltage of the memory cell, apotential difference between the word line WL-US and the semiconductorpillar 75A in the portion 99A is reduced due to channel boosting of thesemiconductor pillar 75A. Thus, a capacitance component of the portion99A is removed from a capacitance component in the selected block. As aresult, a load caused by the semiconductor pillar in the non-selectedstring unit is reduced.

In FIG. 12, a value of the reading voltage VCGRV is set to a constantvalue in order to read 1-bit data. However, if a single memory cellstores data of 2 or more bits, the reading voltage VCGRV may have aplurality of values in order to continuously read data in the memorycell MC by 1 bit.

Time Point t5 a and Time Point t6 a

After the generation of a current in the bit line BL is sensed, eachwiring is disabled at a time point t5 a and a time point t6 a.

At the time point t5 a, the sense amplifier unit 131 sets a potential ofthe bit line BL to the ground voltage VSS.

At the time point t6 a, potentials of the select gate lines SGD, SGM andSGS, and potentials of the word lines WL-S and WL-US are sequentiallyset to the ground voltage VSS.

As mentioned above, in a period from the time point t5 a to the timepoint t6 a, the respective wirings SGD, SGS, SGM, WL, and BL in theselected block BK are disabled. Consequently, reading of data from thememory cell MC is finished.

The sequencer 19 changes a level of the ready/busy signal R/B to an “H”level. Consequently, the memory controller 5 is notified of finishing ofthe read operation in the flash memory 1.

The data read from the memory cell is transmitted from the flash memory1 to the memory controller 5.

As mentioned above, the read operation on the memory cells in the upperarray layer of the flash memory 1 of the present embodiment is finished.

Read Operation on Memory Cell of Lower Array Layer

With reference to FIG. 13, a data read operation on the memory cell ofthe lower array layer will be explained. Reading of data from the memorycell of the lower array layer 110A is different from reading of datafrom the memory cell of the upper array layer 110B in terms of controlon select gate lines of a non-selected string unit in addition tocontrol on a selected word line WL-S.

Time Point T1 b

At a time point t1 b after a command and a selection address arereceived (time point t0), the source line driver 15 applies the groundvoltage VSS to the source line SL (CELSRC).

The row control circuit 12 applies the voltage VSG to selected selectgate lines SGD-S and SGS-S with respect to a selected string unit SU ina selected block BK. In the present embodiment, in the selected stringunit, the row control circuit 12 applies the voltage VSG from the driver129 to the selected intermediate select gate lines SGM-S. Consequently,in the selected string unit, the intermediate select transistors ST3 areturned on, and thus the lower semiconductor pillar 75A is electricallyconnected to the upper semiconductor pillar 75B. In the selected stringunit, the semiconductor pillars 75 are electrically connected to the bitline BL and the source line SL (CELSRC) by turning on the intermediateselect transistors ST1, ST2 and ST3.

If the selected word line WL-S is a word line in the lower array layer110A, the row control circuit 12 applies the ground voltage VSS to thenon-selected drain side select gate lines SGD-US and applies the voltageVSG to the non-selected source side select gate lines SGS-US in thenon-selected string units of the selected block. Consequently, in thenon-selected string units, the transistors ST1 are turned off, and thetransistors ST2 are turned on. In the non-selected string units, the rowcontrol circuit 12 applies the ground voltage VSS to the non-selectedintermediate select gate lines SGM-US. Consequently, in the non-selectedstring units, the intermediate select transistors ST3 are turned off.

As a result, in each of the non-selected string units, the uppersemiconductor pillar 75B is electrically separated from the lowersemiconductor pillar 75A by turning off the intermediate selecttransistors ST3.

Time Point t2 b

At a time point t2 b, the row control circuit 12 starts to apply thereading pass voltage VREAD to the word lines WL-S and WL-US through aspike operation. Potentials of the non-selected word lines WL-US and theselected word line WL-S increase.

In the period TA, electric charge in the semiconductor pillars 75 isreleased to the bit line BL or the source line SL via the turned-ontransistors.

Time Point t3 b

At a time point t3 b, the row control circuit 12 reduces a potentialwhich is equal to or higher than the reading voltage VCGRV to thereading voltage VCGRV in the selected word line WL-S. The senseamplifier circuit 13 charges the bit line BL.

In the non-selected string units, the row control circuit 12 stopsapplication of the voltage VSG to the non-selected source side selectgate lines SGS-US. Consequently, potentials of the non-selected sourceside select gate lines SGS-US are set to the ground voltage VSS, andthus the select transistors ST2 are turned off.

In the selected string unit, a potential of the drain side select gateline SGD-S, a potential of the source side select gate line SGS-S, andpotentials of the intermediate select gate lines SGM-S are maintained tobe the voltage VSG. In the non-selected string units, potentials of thenon-selected intermediate select gate lines SGM-US are maintained to bethe ground voltage VSS.

Time Point t4 b

After the bit line BL is charged in the period TB, at a time point t4 b,a potential of the bit line BL is substantially set to a voltage Vprewith a predetermined magnitude. A potential of the selected word lineWL-S is set to the reading voltage VCGRV, and a potential of thenon-selected word line WL-US is set to the reading pass voltage VREAD.

As described above, the selected cell MC is turned on or off due toapplication of the reading voltage VCGRV, and thus a cell current flowsthrough the bit line BL.

The sense amplifier unit 131 senses the occurrence (or a change in apotential of the node) of a current in the bit line. The sense amplifierunit 131 incorporates a signal corresponding to a result of the sensinginto a latch circuit corresponding to each bit line.

When a threshold voltage of the memory cell in the lower array layer110A is determined, the upper semiconductor pillars 75B of thenon-selected string units SU are subject to channel boosting.

Therefore, data held in the memory cell MC is determined in a state inwhich a capacitance component (load) between the semiconductor pillarand the word line in the upper array layer 110B in each of thenon-selected string units.

Time Point t5 b and Time Point t6 b

At the time point t5 b, the sense amplifier circuit 13 sets a potentialof the bit line BL to the ground voltage VSS.

At the time point t6 b, potentials of the select gate lines SGD, SGM andSGS, and potentials of the word lines WL-S and WL-US are sequentiallyset to the ground voltage VSS.

As mentioned above, in a period from the time point t5 b to the timepoint t6 b, the respective wirings SGD, SGS, SGM, WL, and BL in theselected block BK are disabled, and thus reading of data from theselected cell is finished.

The data read from the memory cell is transmitted from the flash memory1 to the memory controller 5.

As mentioned above, the read operation on the memory cells in the lowerarray layer of the flash memory 1 of the present embodiment is finished.

(b-2-2) Write Operation

With reference to FIG. 14, a write operation of the flash memory of thepresent embodiment will be explained. FIG. 14 is a diagram illustratingvoltage waveforms of the respective wirings during a write operation ofthe flash memory of the present embodiment.

Time Point t20

As illustrated in FIG. 14, at a time point t20, for example, the memorycontroller 5 transmits a writing command, an address (selection address)to which data is to be written, and data to be written, to the flashmemory 1 in response to a request from the host device 600. The flashmemory 1 receives the writing command, the selection address, and thedata. The sequencer 19 starts a write operation based on the writingcommand.

In the flash memory 1, the write operation includes one or more writingloops. If one or more writing loops are executed, the data is writteninto a memory cell included in the selection address.

The writing loops include a program operation and a verificationoperation. Through the program operation, a threshold voltage of amemory cell is shifted in a positive direction. Through the verificationoperation, whether or not a threshold voltage of a memory cell reaches avalue corresponding to data to be written is determined.

The sequencer 19 controls the respective circuits of the flash memory 1so that the write operation is performed as follows.

Time Point t21

During the program operation, at a time point t21, the sense amplifiercircuit 13 starts to control a potential of the bit line BL.

In the sense amplifier circuit 13, the sense amplifier unit 131 appliesthe ground voltage VSS to the bit line BL connected to a memory cellinto which data is to be written. Consequently, the memory cell MC isset to a programmable state (programmable).

In the sense amplifier circuit 13, the sense amplifier unit 131 appliesa voltage V1 to the bit line BL connected to a memory cell into whichdata is not written. Consequently, the memory cell MC is set to aprogramming inhibition state (inhibit). A memory cell set to theprogramming inhibition state is a memory cell which is maintained at an“Er” level, or a memory cell whose threshold voltage reaches a valuecorresponding to data to be written.

The row control circuit 12 starts to control potentials of therespective select gate lines SGD-S, SGD-US, SGS-S, SGS-US, SGM-S andSGM-US.

The row control circuit 12 applies a voltage VSGD to the drain sideselect gate line SGD-S of a selected string unit. The row controlcircuit 12 applies the voltage VSGD to the non-selected drain sideselect gate line SGD-US of a non-selected string unit.

The row control circuit 12 applies a voltage VSGM to the intermediateselect gate lines SGM-S of the selected string unit. The row controlcircuit 12 applies the ground voltage VSS to the non-selectedintermediate select gate lines SGM-US of the non-selected string unit.

The row control circuit 12 applies a voltage VSGS to the source sideselect gate line SGS-S of the selected string unit, and applies theground voltage VSS to the non-selected source side select gate lineSGS-US of the non-selected string unit.

The source line driver 15 applies a voltage V2 to the source line SL(CELSRC).

The voltages VSGD, VSGS and VSGM are voltages for turning on the selecttransistors ST1, ST2 and ST3. Each of the voltages VSGD, VSGS and VSGMis, for example, about 5 V to 6 V. The voltage V1 is, for example, about1.5 V to 2.5 V. The voltage V2 is, for example, about 0.8 V to 1.2 V.

In the selected string unit, the select transistors ST1 and ST3 areturned on, and thus the semiconductor pillars 75 are electricallyconnected to the bit line, in the NAND string 111 of the bit line BL towhich the ground voltage VSS is applied. In the NAND string 111 of thebit line BL to which the voltage V1 is applied, the select transistorST1 is turned off, and thus the bit line BL is electrically separatedfrom the semiconductor pillars 75.

In the non-selected string unit, the select transistor ST1 is turned on,and the select transistor ST3 is turned off. In the non-selected stringunit, the upper semiconductor pillar 75B is connected to the bit lineBL, and the lower semiconductor pillar 75A is electrically separatedfrom the bit line BL.

With respect to the non-selected string unit sharing the intermediateselect gate lines SGM and the source side select gate line SGS with theselected string unit, in the same manner as in the read operation,potentials of the intermediate select gate lines SGM and the source sideselect gate line SGS of the non-selected string unit are the same aspotentials of the intermediate select gate lines SGM and the source sideselect gate line SGS of the selected string unit.

Time Point t22

At a time point t22, the row control circuit 12 starts to control aposition of the word lines WL. The row control circuit 12 applies awriting pass voltage Vpass to the word lines WL.

The row control circuit 12 reduces a potential of the non-selected drainside select gate line SGD-US from the voltage VSGD to the ground voltageVSS. Consequently, the select transistor ST2 of the non-selected drainside select gate line SGD-US is turned off, and thus the semiconductorpillars 75 of the non-selected string unit is electrically separatedfrom the bit line BL.

Time Point t23

At a time point t23, the row control circuit 12 increases a potential ofthe selected word line WL-S from the writing pass voltage Vpass to aprogram voltage VPGM. A potential of the non-selected word line WL-US ismaintained at the writing pass voltage Vpass. A value of the programvoltage VPGM changes with the progress of the write operation. Apredetermined voltage value (step-up voltage) is sequentially added toan initial value of the program voltage VPGM according to the number oftimes of execution of the writing loops.

A threshold voltage of the memory cell of the bit line BL to which theground voltage VSS is applied is shifted in a positive direction as aresult of applying the program voltage VPGM. Consequently, a thresholdvoltage of a programmable memory cell increases.

The select transistor connected to the bit line BL to which the voltageV1 is applied is cut off. Therefore, the memory cell connected to thebit line BL to which the voltage V1 is applied is subject to channelboosting. Consequently, a threshold voltage of the memory cell in aprogramming inhibition state scarcely changes during application of theprogram voltage VPGM.

Time Point t24 to Time Point t26

After a period secured for shifting a threshold voltage of the memorycell (for injecting electric charge into the charge storage layer)elapses, the sequencer 19 reduces a potential of each wiring in order tocomplete the program operation.

At a time point t24, the row control circuit 12 reduces a potential ofthe selected word line WL-S from the program voltage Vpgm to the voltageVpass. At a time point t25, the row control circuit 12 reducespotentials of the selected word line WL-S and the non-selected word lineWL-US from the voltage Vpass to the ground voltage VSS.

Thereafter, at a time point t26, the sense amplifier circuit 13 reducesa potential of the bit line BL to which the voltage V1 is applied, fromthe voltage V1 to the ground voltage VSS.

The row control circuit 12 sets potentials of the selected select gatelines SGD-S, SGS-S and SGM-S to the ground voltage VSS. The source linedriver 15 reduces a potential of the source line SL (CELSRC) from thevoltage V2 to the ground voltage VSS.

Consequently, the program operation in a certain writing loop isfinished.

A verification operation is performed after the program operationillustrated in FIG. 14. The verification operation is similar to theread operation. The verification operation is performed following theprogram operation without a command from the controller 5. Theverification operation is different from the read operation in that averification voltage having one or more verification levels is appliedto the selected word line WL-S instead of a reading voltage. Asmentioned above, in the verification operation, a state of a thresholdvoltage of the memory cell MC is determined. A verification level atwhich data programming is completed may be omitted from the verificationvoltage with the progress of the write operation.

If the selected word line WL-S is a word line WLU in the upper arraylayer 110B in the verification operation, the verification operation isperformed in the substantially same manner as in the read operation inFIG. 12. If the selected word line WL-S is a word line WLL in the lowerarray layer 110A in the verification operation, the verificationoperation is performed in the substantially same manner as in the readoperation in FIG. 13.

A writing loop including the program operation illustrated in FIG. 14and the verification operation illustrated in FIG. 11 or 12 isrepeatedly executed until a threshold voltage of a selected cell reachesa voltage value corresponding to data to be written.

As mentioned above, the write operation of the flash memory of thepresent embodiment is performed.

(b-2-3) Erasing Operation

With reference to FIGS. 15 and 16, an erasing operation of the flashmemory of the present embodiment will be explained.

Block Erasing Operation

FIG. 15 is a diagram illustrating voltage waveforms of the respectivewirings during an erasing operation of the flash memory of the presentembodiment. FIG. 15 illustrates an example in which data of the flashmemory is erased in the block unit.

Time Point t30 a

As illustrated in FIG. 15, for example, at a time point t30 a, thesequencer 19 starts an erasing operation on an erasing target block(selected block) based on a command (a request from the host device)from the memory controller 5 or an internal process of the flash memory1.

Time Point t31 a

At a time point t31 a, the sense amplifier circuit 13 and the sourceline driver 15 start to control potentials of the bit line BL and thesource line SL. The sense amplifier unit 131 applies an erasing voltageVERA to the bit line BL. The source line driver 15 applies the erasingvoltage VERA to the source line SL (CELSRC).

The row control circuit 12 starts to control potentials of the wordlines WL and the respective select gate lines SGD, SGS and SGM in theselected block.

The row control circuit 12 applies a voltage V3 to the drain side selectgate lines SGD of all of the string units and the source side selectgate lines SGS of all of the string units in the selected block. The rowcontrol circuit 12 applies the voltage V3 to the intermediate selectgate lines SGM of all of the string units in the selected block.Consequently, the respective select transistors ST1, ST2 and ST3 areturned on. The voltage V3 is lower than the erasing voltage VERA. Forexample, if the erasing voltage VERA is about 20 V, the voltage V3 isabout 13 V to 15 V.

The row control circuit 12 applies the ground voltage VSS to all of theword lines WL in the selected block.

The erasing voltage VERA is applied to the semiconductor pillars 75 andthe well regions 702 via the bit lines BL and the source lines SL(CELSRC).

As mentioned above, during the erasing operation, a potential of thesemiconductor pillar 75 is higher than a potential of the word line WL.Consequently, electric charge in the charge storage layer 792 isreleased to the semiconductor pillar 75. As a result, the memory cell isset to an erasing state (“Er” level).

Time Point t32 a

At a time point t32 a, the row control circuit 12 reduces potentials ofthe select gate lines SGD, SGS and SGM from the voltage V3 to the groundvoltage VSS.

In the sense amplifier circuit 13, the sense amplifier unit 131 reducesa potential of the bit line BL from the erasing voltage VERA to theground voltage VSS. The source line driver 15 reduces a potential of thesource line SL (CELSRC) from the erasing voltage VERA to the groundvoltage VSS.

Consequently, the erasing operation in the block unit in the flashmemory is finished.

Division Erasing Operation

FIG. 16 is a diagram illustrating voltage waveforms of the respectivewirings during an erasing operation of the flash memory of the presentembodiment. As described above, the flash memory may erase data in theunit smaller than a block. FIG. 16 illustrates an example in which dataof the flash memory is erased in the predetermined control unit in ablock.

Time Point t30 b

As illustrated in FIG. 16, for example, at a time point t30 b, thesequencer 19 starts an erasing operation based on a command (a requestfrom the host device) from the memory controller 5 or an internalprocess of the flash memory 1.

For example, if a partial erasing operation is performed, in a selectedblock, one of control units for partial erasing, set in the block, isselected. The control unit includes one or more word lines.

Time Point t31 b

At a time point t31 b, the sense amplifier unit 131 applies an erasingvoltage VERA to the bit line BL in the same manner as in the blockerasing operation. The source line driver 15 applies the erasing voltageVERA to the source line SL (CELSRC). The row control circuit 12 appliesthe voltage V3 to the drain side select gate lines SGD of all of thestring units SU, the source side select gate lines SGS of all of thestring units SU, and the intermediate select gate lines SGM of all ofthe string units SU, in the selected block.

In the partial erasing operation, the row control circuit 12 applies theground voltage VSS to word lines WL-S included in an erasing targetcontrol unit (selected control unit) in the selected block.

The row control circuit 12 applies the erasing voltage VERA to wordlines WL-US included in a control unit (non-selected control unit) otherthan the erasing target.

A control unit (number of selected word lines) for partial erasing maybe a single array layer unit, and may be a unit smaller than the arraylayer. A partial erasing unit may be larger than the array layer.

In the erasing target control unit, electric charge in the chargestorage layer is released to the semiconductor pillar 75 due to apotential difference between the semiconductor pillar 75 and the wordline WL-S. As a result, memory cells included in the erasing targetcontrol unit are set to an erasing state.

On the other hand, in a non-selected control unit, since the erasingvoltage VERA is applied to the word lines WL-US, a potential differencebetween the semiconductor pillar 75 and the word line WL is scarcelygenerated. As a result, regarding memory cells included in thenon-selected control unit in the partial erasing operation, a thresholdvoltage of the memory cell MC scarcely changes and is thus maintained toa voltage value before the erasing operation is performed.

Time Point t32 b

At a time point t32 b, the row control circuit 12 reduces potentials ofthe word lines WL-US included in the non-selected control unit from theerasing voltage VERA to the ground voltage VSS.

In the same manner as in the block erasing operation, potentials of theselect gate lines SGD, SGS and SGM, a potential of the bit line BL, anda potential of the source line SL (CELSRC) are set to the ground voltageVSS.

Consequently, the erasing operation on the control unit smaller than theblock in the flash memory is finished.

As mentioned above, in the partial erasing operation of the flashmemory, data is erased in an erasing target control unit in a selectedblock. On the other hand, in the selected block, a non-erasing targetcontrol unit holds data before the partial erasing operation.

In the above-described way, in the flash memory of the presentembodiment, data held in a certain portion of a block is selectivelyerased.

(c) Summary

In the flash memory of a memory device of the present embodiment, thememory cell array includes a plurality of stacked array layers. In thiscase, the NAND string has a structure in which a plurality ofsemiconductor pillars are stacked.

In the flash memory of the present embodiment, not only the drain sideand source select gate lines but also the intermediate select gate linesare connected to the NAND string. The intermediate select gate lines areprovided in a region near the junction of the stacked semiconductorpillars. The NAND string includes not only the select transistorsprovided at one end and the other end of the NAND string, but also theselect transistors connected to the intermediate select gate lines.

In the flash memory of the present embodiment, the conductive layers areprovided to oppose the side surfaces of the semiconductor pillars in theregion near the junction of a plurality of semiconductor pillars. Theconductive layers are used as the select gate lines (intermediate selectgate lines). The select transistors are provided in a portion where theintermediate select gate lines oppose the semiconductor pillars.

Consequently, the flash memory of the present embodiment can control anelectrical conduction state between the semiconductor pillar of thelower array layer and the semiconductor pillar of the upper array layerby controlling potentials of the intermediate select gate lines.

The flash memory of the present embodiment can electrically connect asemiconductor pillar in an array layer including a selected word line,among a plurality of array layers and among a plurality of semiconductorpillars included in the NAND string, to a bit line or a source line, ina non-selected string unit, and can electrically separate thesemiconductor pillars in the other array layers from the bit line or thesource line.

Consequently, regarding a semiconductor pillar connected to the bit lineor the source line, electric charge in the semiconductor pillar can beremoved.

Therefore, the flash memory of the present embodiment can reduce theoccurrence of reading disturbance.

The flash memory of the present embodiment can cause a semiconductorpillar of an electrically separated portion among the plurality ofstacked array layers, to be subject to channel boosting. Consequently,the flash memory of the present embodiment can prevent the occurrence ofa capacitance component during an operation.

Therefore, the flash memory of the present embodiment can reduce a loadcaused by a capacitance component of a semiconductor pillar and can thusreduce a current (load current) caused by the load. As a result, theflash memory of the present embodiment can reduce a peak value of acurrent generated in a memory cell array, suppress an increase in powerconsumption, and prevent deterioration in an operation speed.

The flash memory of the present embodiment can electrically separate theupper array layer and the lower array layer from each other bycontrolling a potential of the select gate line (turning-on andturning-off of the select transistor), and can thus suppress an increasein the number of dummy word lines for securing a distance betweenelements. Consequently, the flash memory of the present embodiment canrealize improvement of memory density in a memory cell array, areduction in the number of wirings, a reduction in a thickness (adimension in the D3 direction) of a memory cell array, and the like. Asa result, the flash memory of the present embodiment can reduce chipcost of the flash memory.

As mentioned above, the memory device of the present embodiment canimprove operation characteristics.

(2) Second Embodiment

With reference to FIGS. 17 and 18, a memory device and a control methodtherefor according to a second embodiment will be explained.

In a flash memory of the second embodiment, a voltage sensing method(bit line shield method) is used for a determination of a thresholdvoltage of a memory cell.

In the voltage sensing method, a change in a potential of a bit line dueto turning-on or turning-off of a memory cell is sensed, and thus astate of a threshold voltage of the memory cell is determined.

Fundamental configurations of a circuit and a structure of the flashmemory of the present embodiment are substantially the same as theconfigurations of the flash memory of the first embodiment. However, inthe flash memory using the voltage sensing method, a single senseamplifier unit 131 may control two bit lines (even-numbered andodd-numbered bit lines) adjacent to each other.

(2a) Operation Example

Read Operation on Memory Cell of Upper Array Layer

FIG. 17 is a diagram illustrating voltage waveforms of the respectivewirings during a read operation of the flash memory of the presentembodiment.

Time Point t11 a

As illustrated in FIG. 17, in the same manner as in data reading in theflash memory using the current sensing method, at a time point t0, thesequencer 19 starts a data read operation based on a reading command anda selection address from the memory controller 5.

At a time point t11 a, the row control circuit 12 starts to controlpotentials of the drain side select gate lines SGD-S and SGD-US, andpotentials of the intermediate select gate lines SGM-S and SGM-US.

The row control circuit 12 applies the voltage VSG to the source sideselect gate line SGS-S of a selected string unit. The row controlcircuit 12 applies the ground voltage VSS to the non-selected sourceside select gate line SGS-US of a non-selected string unit.

Time Point t12 a and Time Point t13 a

At a time point t12 a, the row control circuit 12 starts to apply avoltage to the word lines WLU and WLL.

In a period TA from the time point t12 a to the time point t13 a, thevoltage VSG is applied to the non-selected drain side select gate lineSGD-US, and thus the select transistor ST1 is turned on. Consequently,the semiconductor pillar 75B of the upper array layer 110B of thenon-selected string unit is electrically connected to the bit line BLvia the transistor ST1 in the on state. As a result, not only residualelectric charge in the semiconductor pillars 75 of the selected stringunit but also residual electric charge in the semiconductor pillar 75Bof the upper array layer 110B of the non-selected string unit arereleased to the bit line BL.

In the period TA, in the non-selected string unit SU, the ground voltageVSS is applied to the non-selected source side select gate line SGS-USand the intermediate select gate lines SGM, and thus the selecttransistors ST2 and the select transistor ST3 are turned off. Therefore,in the period TA, the semiconductor pillar 75A of the lower array layer110A is electrically separated from the bit line BL and the source lineSL (CELSRC) and is thus in an electrically floating state.

At the time point t13 a, the row control circuit 12 controls theselected word line WL-S in order to set a potential of the selected wordline WL-S of the upper array layer 110B to the reading voltage VCGRV.The sense amplifier unit 131 starts to apply a voltage to the bit lineBL. Here, if a single sense amplifier unit 131 controls two bit lines,the sense amplifier unit 131 charges one bit line (for example, anodd-numbered bit line) and applies the ground voltage VSS to the otherbit line (for example, an even-numbered bit line).

The row control circuit 12 reduces a potential of the non-selected drainside select gate line SGD-US of the non-selected string unit from thevoltage VSGD to the ground voltage VSS. The potential of the selecteddrain side select gate line SGD-S is maintained to be the voltage VSG.

The row control circuit 12 controls the selected word line WL-S and thebit line BL, and also reduces a potential of the source side select gateline SGS-S from the voltage VSG to the ground voltage VSS. Since theground voltage VSS is applied, the select transistor ST2 of the sourceside select gate line SGS-S is turned off. The bit line BL and thesemiconductor pillars 75 are electrically separated from the source lineSL (CELSRC) by turning off the select transistor ST2, and thus the bitline BL and the semiconductor pillars 75 are charged.

Time Point t14 a

In a period TB from the time point t13 a to a time point t14 a, the bitline BL is charged to a desired potential Vpre.

At the time point t14 a, a potential of the selected word line WL-S isset to the reading voltage VCGRV. The row control circuit 12 increases apotential of the source side select gate line SGS-S from the groundvoltage VSS to the voltage VSG.

In the selected string unit, if the potential of the source side selectgate line SGS-S reaches the voltage VSG, the select transistor ST2 isturned on, and thus the source line SL (CELSRC) is electricallyconnected to the semiconductor pillar 75B. At this time, in thenon-selected string unit, the lower semiconductor pillar 75A is subjectto channel boosting.

When the reading voltage VCGRV is applied, if the selected cell isturned on, the bit line BL is electrically connected to the source lineSL (CELSRC), and thus the bit line is discharged. Consequently, apotential of the bit line BL is reduced from the voltage Vpre. The senseamplifier unit 131 senses that the potential of the bit line BL isreduced.

When the reading voltage VCGRV is applied, if the selected cell isturned off, the bit line BL is electrically separated from the sourceline SL (CELSRC). Consequently, a potential of the bit line BL ismaintained to be the voltage Vpre. The sense amplifier unit 131 sensesthat the potential of the bit line BL is maintained.

As mentioned above, in the data read operation using the voltage sensingmethod, each sense amplifier unit 131 senses whether or not a potentialof the bit line BL changes. Consequently, data held in the memory cellMC is determined.

During a determination of a threshold voltage of the memory cell, thelower semiconductor pillar of the non-selected string unit is subject tochannel boosting, and thus a load caused by a capacitance component ofthe lower semiconductor pillar is reduced.

Time Point t15 a to Time Point t16 a

At a time point t15 a, the sense amplifier unit 131 reduces a potentialof the bit line BL from the voltage Vpre to the ground voltage VSS.

At a time point t16 a, the row control circuit 12 reduces potentials ofthe select gate lines SGD-S, SGM-S and SGS-S from the voltage VSG to theground voltage VSS. The row control circuit 12 reduces a potential ofthe selected word line WL-S from the voltage VCGRV to the ground voltageVSS, and reduces a potential of the non-selected word line WL-US fromthe reading pass voltage VREAD to the ground voltage VSS.

Consequently, reading of data from the memory cell of the upper arraylayer 110B is finished.

Read Operation on Memory Cell of Lower Array Layer

With reference to FIG. 18, reading of data from the memory cell of thelower array layer in the flash memory using the voltage sensing methodwill be explained. FIG. 18 is a diagram illustrating voltage waveformsof the respective wirings during a read operation of the flash memory ofthe present embodiment.

Time Point t11 b

As illustrated in FIG. 18, in the same manner as in the exampleillustrated in FIG. 17, after a data read operation is started based ona reading command and a selection address (time point t0), at a timepoint t11 b, the row control circuit 12 applies the voltage VSG to therespective select gate lines SGD-S, SGS-S and SGM-S of a selected stringunit.

If the word line WLL of the lower array layer 110A is selected, the rowcontrol circuit 12 applies the ground voltage VSS to the non-selecteddrain side select gate line SGD-US of a non-selected string unit. Therow control circuit 12 applies the voltage VSG to the source side selectgate line SGS-S of the selected string unit and also to the non-selectedsource side select gate lines SGS-US of the non-selected string unit.The row control circuit 12 applies the ground voltage VSS to thenon-selected intermediate select gate lines SGM-US of the non-selectedstring unit.

Time Point t12 b and Time Point t13 b

At a time point t12 b, the row control circuit 12 starts to apply thereading pass voltage VREAD to the word lines WLU and WLL.

In a period TA (a time point t12 b to a time point t13 b), the voltageVSG is applied to the source side select gate line SGS-S, and thus theselect transistor ST2 is turned on. Consequently, the semiconductorpillar 75A of the lower array layer 110A of the non-selected string unitis electrically connected to the source line SL (CELSRC). As a result,not only residual electric charge in the semiconductor pillars 75 of theselected string unit but also residual electric charge in thesemiconductor pillar 75A of the non-selected string unit are released tothe source line SL (CELSRC) (or the well region).

In the period TA, the ground voltage VSS is applied to the intermediateselect gate lines SGM-S. Consequently, the semiconductor pillar 75B ofthe upper array layer 110B of the non-selected string unit iselectrically separated from the source line SL (CELSRC). In the upperarray layer 110B, the semiconductor pillar 75B is in an electricallyfloating state.

At the time point t13 b, the sense amplifier unit 131 starts to chargethe bit line BL. The row control circuit 12 reduces potentials of theselected source side select gate line SGS-S and the non-selected sourceside select gate line SGS-US from the voltage VSG to the ground voltageVSS. The row control circuit 12 applies the reading voltage VCGRV to theselected word line WL-S in the lower array layer 110A.

Time Point t14 b

At a time point t14 b, the row control circuit 12 increases a potentialof the source side select gate line SGS-S from the ground voltage VSS tothe voltage VSG. Since the select transistor ST2 is turned on, thesource line SL (CELSRC) is electrically connected to the semiconductorpillar 75A.

The reading voltage VCGRV is applied, and thus the selected cell isturned on or off. A change in a potential of the bit line BL due toturning-on or turning-off of a selected cell is sensed by the senseamplifier unit 131. As a result, data held in the memory cell MC isdetermined.

In a period TC, in a determination of data held in the memory cell, thesemiconductor pillar 75B of the upper array layer 110B of thenon-selected string unit is subject to channel boosting, and thus acapacitance component between the semiconductor pillar 75B and the wordline WLU is scarcely generated.

Time Point t15 b to Time Point t16 b

At a time point t15 b, the sense amplifier unit 131 reduces a potentialof the bit line BL to the ground voltage VSS.

At a time point t16 b, the row control circuit 12 reduces potentials ofthe select gate lines SGD-S, SGM-S and SGS-S to the ground voltage VSS.The row control circuit 12 reduces potentials of the selected word lineWL-S and the non-selected word line WL-US to the ground voltage VSS.

Consequently, reading of data from the memory cell of the lower arraylayer 110A is finished.

In the present embodiment, a data write operation and a data erasingoperation are performed in the same manner as in the first embodiment.During a write operation, the operations illustrated in FIGS. 17 and 18correspond to a verification operation.

As mentioned above, the flash memory of the present embodiment canreduce reading disturbance during an operation even if the voltagesensing method is applied to a determination of a threshold voltage ofthe memory cell in a read operation (and a verification operation) ofthe flash memory, and can also reduce a capacitance component of acertain portion in a selected block. As a result, a load caused by acapacitance component of the semiconductor pillar can be reduced.

Therefore, the flash memory of the present embodiment can achieve thesame effect that the effect in the first embodiment.

Therefore, the flash memory of the second embodiment can improveoperation characteristics.

(3) Third Embodiment

With reference to FIG. 19, a memory device and a control method thereforaccording to a third embodiment will be explained.

FIG. 19 is a diagram illustrating voltage waveforms of the respectivewirings during a read operation (or a verification operation) of a flashmemory of the present embodiment.

In the present embodiment, in the flash memory using the current sensingmethod, a timing of applying a voltage to a non-selected word line ofthe upper array layer and a timing of applying a voltage to anon-selected word line of the lower array layer are different from eachother.

Operation Example

Read Operation on Memory Cell of Upper Array Layer

Time Point t1 c and Time Point t2 c

As illustrated in FIG. 19, after reading of data is started, at a timepoint t1 c, the voltage VSG is applied to the drain side select gatelines SGD-S and SGD-US, and the selected intermediate select gate linesSGM-S.

At a time point t2 c, if a word line WL in the upper array layer 110B isselected, a voltage starts to be applied to the selected word line WL-S,and a non-selected word line WL-US in the upper array layer 110B.

In the present embodiment, application of a voltage to the word line WLLin the lower array layer 110A is performed at a timing which isdifferent from a timing at which a voltage is applied to a word line WLUin the upper array layer 110B including the selected word line WL-S.

Therefore, at the time point t2 c, a voltage does not start to beapplied to the word line WLL, and a potential of the word line WLL ismaintained to be the ground voltage VSS.

Since the potential of the word line WLL is maintained to be the groundvoltage VSS, the selected source side select gate line SGS-S ismaintained to be the ground voltage VSS.

The memory cell in the lower array layer 110A is turned off since theground voltage VSS is applied to the word line WLL. The elements and thewirings of the upper array layer 110B are electrically separated fromthe source line SL (CELSRC) by turning off the memory cells MC of thelower array layer 110A regardless of turning-on and turning-off of theselect transistor ST2 of the selected source side select gate lineSGS-S.

If the ground voltage VSS is applied, and thus the memory cell MC of theword line WLL is turned off, an adverse effect does not occur in a readoperation even if a potential of the selected source side select gateline SGS-S is maintained to be the ground voltage VSS when a voltagestarts to be applied to the selected word line WL-S of the upper arraylayer 110B.

Time Point t3 c to Time Point t5 c

After a release process in a period TA (the time point t2 c to a timepoint t3 c), at the time point t3 c, the reading pass voltage VREADstarts to be applied to a word line (non-selected word line) WLL of thelower array layer 110A. In a selected string unit, the voltage VSGstarts to be applied to the source side select gate line SGS-S.

Consequently, in a period TB from the time point t3 c to the time pointt4 c, a potential of the word line WLL is set to the reading passvoltage VREAD, and a potential of the selected source side select gateline SGS-S is set to the voltage VSG, along with charging of the bitline BL.

In a period TC from the time point t4 c to a time point t5 c, thegeneration of a cell current due to turning-on or turning-off of aselected cell is sensed by the sense amplifier unit 131 in a state inwhich the lower semiconductor pillar 75A of the non-selected string unitis subject to a channel boosting. Consequently, data held in theselected cell is read.

Thereafter, at the time point t5 c and a time point t6 c, the word linesWL and the select gate lines SGD, SGS and SGM are disabled, and thus theread operation of the flash memory 1 is completed.

If the word line WLL of the lower array layer 110A is selected, avoltage starts to be applied to the word line WLL of the lower arraylayer 110A at the time point t2 c in FIG. 19. Thereafter, a voltagestarts to be applied to the word line WLU of the upper array layer 110Bat the time point t3 c in FIG. 19.

In this case, in the selected and non-selected string units, timings ofapplying voltages to the select gate lines SGD, SGS and SGM are the sameas the timings illustrated in FIG. 13. However, in the period TA, theground voltage VSS may be applied to the select gate lines SGD-S andSGM-S of the selected string unit.

As mentioned above, in the flash memory of the present embodiment, evenif timings of control on the word lines are different from each other,the substantially same effects as the effects in the above-describedembodiments can be achieved.

(4) Fourth Embodiment

With reference to FIG. 20, a memory device according to a fourthembodiment will be explained.

FIG. 20 is a diagram illustrating voltage waveforms of the respectivewirings during a read operation (or a verification operation) of a flashmemory of the present embodiment.

In the present embodiment, in the flash memory using the voltage sensingmethod, a timing of applying a voltage to a non-selected word line ofthe upper array layer and a timing of applying a voltage to anon-selected word line of the lower array layer are different from eachother.

Operation Example

Read Operation on Memory Cell of Upper Array Layer

Time Point t11 c and Time Point t12 c

As illustrated in FIG. 20, at a time point t11 c, the voltage VSG isapplied to the drain side select gate lines SGD-S and SGD-US and SGM-Sin the same manner as in the example illustrated in FIG. 19.

At a time point t12 c, the word line WLU of the upper array layer 110Bis selected based on a selection address. A voltage starts to be appliedto the word line WLU. A potential of the word line WLL of the lowerarray layer 110A is maintained to be the ground voltage VSS.

In a period TA from the time point t11 c to a time point t13 c,potentials of the source side select gate lines SGS-S and SGS-US of theselected string unit and the non-selected string unit are maintained tobe the ground voltage VSS. Since the memory cell of the lower arraylayer 110A is turned off, the source side select transistor ST2 of theNAND string 111 may be turned off.

In the period TA, electric charge in the semiconductor pillars 75A and75B is released to the bit line BL via the turned-on drain side selecttransistor ST1.

Time Point t13 c

At the time point t13 c, the bit line starts to be charged.

A potential of the non-selected drain side select gate line SGD-US ofthe non-selected string unit transitions from the voltage VSG to theground voltage VSS.

The reading pass voltage VREAD is applied to the word line (non-selectedword line) WLL (WL-US) of the lower array layer 110A.

In a period TB from the time point t12 c to the time point t13 cfollowing the period TA, potentials of the source side select gate linesSGS-S and SGS-US are maintained to be the ground voltage VSS.

Time Point t14 c to Time Point t15 c

At a time point t14 c, in the selected string unit, the voltage VSG isapplied to the source side select gate line SGS-S. The select transistorST2 connected to the source side select gate line SGS-S is turned on.The source line SL (CELSRC) is electrically connected to the NAND string111 of the selected string unit via the turned-on select transistor ST2.

In a period TC from the time point t14 c to a time point t15 c, a changein a potential of the bit line BL due to turning-on or turning-off of aselected cell is sensed by the sense amplifier unit 131. As a result,data held in the selected cell is read.

Since the lower pillar of the non-selected string unit is subject tochannel boosting when a potential of the bit line BL is sensed, a loadcaused by a capacitance component of the semiconductor pillar isreduced.

If the word line WLL of the lower array layer 110A is selected, voltagesstart to be applied to the selected and non-selected word lines WLL ofthe lower array layer 110A at the time point t12 c in FIG. 20, and avoltage starts to be applied to the word line WLU of the upper arraylayer 110B at the time point t13 c in FIG. 20. In this case, timings ofapplying voltages to the select gate lines SGD, SGS and SGM are the sameas in the example illustrated in FIG. 18. However, in the period TA, theground voltage VSS may be applied to the select gate lines SGD-S andSGM-S of the selected string unit.

As mentioned above, a read operation on the memory cell of the lowerarray layer 110A is performed.

As mentioned above, even if timings of control on the word lines aredifferent from each other, the flash memory of the present embodimentcan improve operation characteristics in a voltage sensing type flashmemory.

(5) Fifth Embodiment

With reference to FIGS. 21 and 22, a memory device and a control methodtherefor according to a fifth embodiment will be explained. FIGS. 21 and22 are diagrams illustrating voltage waveforms of the respective wiringsduring a read operation (or a verification operation) of a flash memoryof the present embodiment.

During a data read operation of the flash memory, a voltage VSRC higherthan the ground voltage VSS may be applied to the source line SL(CELSRC). Since the positive voltage VSRC is applied to the source line(and the well region), even if a part of a threshold voltage valuedistribution corresponding to data is present in a negative voltageregion, a threshold voltage of the memory cell may be regarded as havinga positive voltage value due to a relative potential relationship.

Hereinafter, in the read operation of the flash memory, an operationexample of the flash memory of the present embodiment if a certainvoltage VSRC (VSRC>VSS) is applied to the source line SL will beexplained. In the present embodiment, a determination of a thresholdvoltage of each memory cell in the flash memory is performed by usingthe current sensing method.

Operation Example

Read Operation on Upper Array Layer

Time Point t1 d

As illustrated in FIG. 21, at a time point tld, the voltage VSG isapplied to the drain side select gate lines SGD-S and SGD-US, and thesource side select gate line SGS-S of a selected string unit.

In the present embodiment, the source line driver 15 applies the sourceline voltage VSRC to the source line SL (CELSRC). The voltage VSRC ishigher than the ground voltage VSS. For example, the voltage VSRC islower than the voltage VSG.

If the voltage VSRC is applied to the source line SL (CELSRC), the rowcontrol circuit 12 applies the voltage VSRC to the non-selected sourceside select gate line SGS-US and the non-selected intermediate selectgate lines SGM-US of a non-selected string unit.

Since the voltage VSG is sufficiently higher than the voltage VSRC, evenif the voltage VSRC is applied to the sources or the drains of thetransistors ST1, ST2 and ST3, and the select transistors ST1, ST2 andST3 of which the voltage VSG is applied to the gates are turned on. Avoltage higher than the voltage VSG may be applied to the select gatelines SGD, SGS and SGM in consideration of application of the voltageVSRC.

For example, at the time point t1 d, the sense amplifier unit 131applies the voltage VSRC to the bit line BL. Since a potential of thebit line BL is set to be the same as a potential of the source line SL(CELSRC), a through-current can be prevented from flowing through theNAND string 111. However, in a period TA, a potential of the bit line BLmay be set to the ground voltage VSS.

In the non-selected string unit, if the voltage VSRC is applied to thesource or the drain of the transistor although the voltage VSRC isapplied the gate thereof, the potentials of the gate and the source orthe drain are substantially the same as each other, and thus the selecttransistors ST1, ST2 and ST3 are turned off.

Time point t2 d to time point t3 d

At a time point t2 d, voltages start to be applied to the word lines WLUand WLL. In the same manner as in the above-described embodiments, inthe period TA, residual electric charge is released from thesemiconductor pillars 75 to the bit line BL or the source line SL(CELSRC) via the turned-on select transistors ST1 and ST2. In thenon-selected string unit, the semiconductor pillar 75A of the lowerarray layer 110A is electrically separated from the bit line BL and thesource line SL (CELSRC) by turning off the select transistors ST2 andST3.

At a time point t3 d, among a plurality of word lines WLU and WLL, apotential of the selected word line WL-S of the upper array layer 110Bis controlled to be set to the reading voltage VCGRV. A potential of thenon-selected drain side select gate line SGD-US is reduced from thevoltage VSG to the voltage VSRC.

In the period TA, if a potential of the bit line BL is set to the groundvoltage VSS, the bit line BL starts to be charged at the time point t3d.

Time Point T4 d to Time Point t6 d

In a period TC from a time point t4 d to a time point t5 d, thegeneration of a current in the bit line BL is sensed. In the period TC,potentials of the source line SL (CELSRC) and the non-selected selectgate lines SGD-US, SGM-US and SGS-US are maintained to be the voltageVSRC.

In the period TC, in the non-selected string unit, the semiconductorpillar 75A of the lower array layer 110A is subject to channel boosting,and thus a capacitance component between the word line WL and thesemiconductor pillar 75A is scarcely generated. Therefore, a state of athreshold voltage of the memory cell is determined in a state in which aload caused by a parasitic capacitance of the semiconductor pillar 75Ais reduced.

At a time point t5 d, a potential of the bit line BL is set to theground voltage VSS.

At a time point t6 d, potentials of the word lines WLU and WLL, andpotentials of the select gate lines SGD, SGM and SGS are set to theground voltage VSS.

In a period from the time point t3 d to the time point t6 d, a potentialof the source line SL (CELSRC), and potentials of the non-selectedselect gate lines SGD-US, SGM-US and SGS-US are maintained to be thevoltage VSRC.

At the time point t6 d, the source line driver 15 controls the sourceline CELSRC so as to set a potential of the source line SL (CELSRC) tothe ground voltage VSS. The row control circuit 12 sets potentials ofthe non-selected select gate lines SGD-US, SGM-US and SGS-US to theground voltage VSS.

Consequently, in the flash memory of the present embodiment, reading ofdata from the memory cell MC of the upper array layer 110B is finished.

Read Operation on Memory Cell of Lower Array Layer

With reference to FIG. 22, a data read operation on the memory cell ofthe lower array layer will be explained.

Time Point t1 e

During a read operation on the lower array layer 110A, at a time pointt1 e, the voltage VSRC is applied to the source line SL (CELSRC), andthe non-selected drain side select gate lines SGD-US and SGM-US of anon-selected string unit. The voltage VSG is applied to the non-selectedsource side select gate line SGS-US of the non-selected string unit.

Potentials of the select gate lines SGD-S, SGS-S and SGM-S of a selectedstring unit are controlled in the same manner as in the exampleillustrated in FIG. 21.

Time Point t2 e to Time Point t3 e

At a time point t2 e, voltages start to be applied to the word lines WLUand WLL.

In a period TA, residual electric charge is released to the bit line BLor the source line SL (CELSRC) via the turned-on select transistors ST1,ST2 and ST3.

At a time point t3 e, a potential of the selected word line WL-S of thelower array layer 110A is set to the reading voltage VCGRV, and apotential of the non-selected source side select gate line SGS-US is setto the voltage VSRC.

Time Point Toe to Time Point t6 e

After the bit line BL is charged to the predetermined voltage Vpre, acurrent of the bit line BL is sensed in a period TC in the same manneras in the example illustrated in FIG. 21. In the period TC, the uppersemiconductor pillar 75B of the non-selected string unit is subject tochannel boosting, and thus a load caused by a capacitance component ofthe upper semiconductor pillar 75B is reduced.

Thereafter, at a time point t5 e and a time point t6 e, potentials ofthe respective wirings are set to the ground voltage VSS.

As mentioned above, reading of data from the memory cell of the lowerarray layer 110A in the flash memory of the present embodiment isfinished.

An operation similar to the operation illustrated in FIG. 21 or 22 isalso applied to a verification operation, and thus a state of athreshold voltage of a memory cell in a write operation can bedetermined.

As in the present embodiment, even if a read operation (or averification operation) is performed in a state in which the voltageVSRC higher than the ground voltage is applied to the source line SL(CELSRC), the flash memory of the present embodiment can improveoperation characteristics.

(6) Sixth Embodiment

With reference to FIGS. 23 and 24, a memory device and a control methodtherefor according to a sixth embodiment will be explained. FIGS. 23 and24 are diagrams illustrating voltage waveforms of the respective wiringsduring a read operation (or a verification operation) of a flash memoryof the present embodiment.

If a read operation (or a verification operation) of the flash memory isperformed according to the voltage sensing method, the voltage VSRC maybe applied to the source line SL.

Hereinafter, a description will be made of an example in which the flashmemory of the present embodiment performs a determination of a thresholdvoltage of a memory cell according to the voltage sensing method in astate in which the voltage VSRC is applied to the source line SL.

Operation Example

Read Operation on Upper Array Layer

With reference to FIG. 23, a read operation on a memory cell of theupper array layer according to the voltage sensing method in the flashmemory of the present embodiment will be explained.

Time Point t11 d to Time Point t12 d

As illustrated in FIG. 23, at a time point t11 d, the voltage VSG isapplied to the drain side select gate lines SGD-S and SGD-US, the sourceside select gate line SGS-S, and non-selected the intermediate selectgate lines SGM-US. In a non-selected string unit, the voltage VSRC isapplied to the non-selected intermediate select gate lines SGM-US andthe non-selected source side select gate line SGS-US.

The voltage VSRC is applied to the source line SL (CELSRC). For example,the voltage VSRC is applied to the bit line BL.

As described above, the select transistors ST1, ST2 and ST3 of aselected string unit are turned on, and the drain side select transistorST1 of the non-selected string unit is turned on.

In a period TA (the time point t12 d to a time point t13 d), electriccharge in the semiconductor pillars 75 is released to the bit line BL orthe source line SL (CELSRC) via the turned-on select transistors ST1,ST2 and ST3.

Time Point t13 d

At the time point t13 d, the bit line BL starts to be charged.

A potential of the source side select gate line SGS-S is reduced fromthe voltage VSG to the voltage VSRC. Consequently, the select transistorST2 connected to the source side select gate line SGS-S is turned off,and, in the selected string unit, the bit line BL and the semiconductorpillars 75 are charged in a state of being electrically separated fromthe source line SL (CELSRC).

A potential of the non-selected drain side select gate line SGD-US isreduced from the voltage VSG to the voltage VSRC, and thus the selecttransistor ST1 is turned off.

A potential of the selected word line WL-S of the upper array layer 110Bis set to the reading voltage VCGRV.

Time Point t14 d

At a time point t14 d, in the selected string unit, a potential of thesource side select gate line SGS-S is increased from the voltage VSRC tothe voltage VSG. Consequently, the select transistor ST2 is turned on,and thus the lower semiconductor pillar 75A is electrically connected tothe source line SL (CELSRC).

In a period TC, a potential of the bit line BL is sensed, and thus dataheld in the memory cell of the upper array layer 110B is read. In thiscase, in the non-selected string unit, the semiconductor pillar 75A ofthe lower array layer 110A is subject to channel boosting, and thus acapacitance component between the semiconductor pillar 75A and the wordline WLL is reduced.

Time Point t15 d and Time Point t16 d

At a time point t15 d, charging of the bit line BL is stopped, and apotential of the bit line BL is set to the ground voltage VSS.

At a time point t16 d, potentials of the word lines WLU and WLL, andpotentials of the selected select gate lines SGD-S, SGM-S and SGS-S areset to the ground voltage VES. Potentials of the non-selected selectgate lines SGD-US, SGM-US and SGS-US are set to the ground voltage VSS.

The source line driver 15 sets a potential of the source line SL(CELSRC) to the ground voltage VSS.

As mentioned above, reading of data from the memory cell of the upperarray layer 110B in the flash memory of the present embodiment isfinished.

Read Operation on Memory Cell of Lower Array Layer

With reference to FIG. 24, a read operation on a memory cell of thelower array layer according to the voltage sensing method in the flashmemory of the present embodiment will be explained.

Time Point t11 e and Time Point t12 e

As illustrated in FIG. 24, at a time point t11 e, the voltage VSG isapplied not only to the respective select gate lines SGD-S, SGS-S andSGM-S of a selected string unit but also to the non-selected source sideselect gate line SGS-US of a non-selected string unit.

The voltage VSRC is applied to the non-selected drain side select gateline SGD-US and the non-selected intermediate select gate lines SGM-US.

In the same manner as in the example illustrated in FIG. 23, the voltageVSRC is applied to the source line SL (CELSRC) and the bit line BL.

In a period TA, electric charge in the semiconductor pillars 75 isreleased to the bit line BL or the source line SL (CELSRC) via theturned-on select transistors ST1, ST2 and ST3.

In this case, in the non-selected string unit SU, the uppersemiconductor pillar 75B is electrically separated from the bit line BLand the lower semiconductor pillar 75A.

Time Point t13 e

At a time point t13 e, in order to charge the bit line BL and thesemiconductor pillars 75, potentials of the source side select gatelines SGS-S and SGS-US are reduced from the voltage VSG to the voltageVSRC. Consequently, the source side select transistors ST2 are turnedoff.

The selected word line WL-S of the lower array layer 110A is reduced tothe reading voltage VCGRV.

Time Point t14 e to Time Point t16 e

At a time point t14 e, in the selected string unit, a potential of thesource side select gate line SGS-S is increased from the voltage VSRC tothe voltage VSG. Consequently, the select transistor ST2 is turned on,and thus the lower semiconductor pillar 75A is electrically connected tothe source line SL (CELSRC).

A state of a potential of the bit line BL corresponding to turning-onand turning-off of a selected cell is sensed, and thus data held in thememory cell of the lower array layer 110A is read.

When the data held in the memory cell of the lower array layer 110A isread, in the non-selected string unit, the semiconductor pillar 75B ofthe upper array layer 110B is subject to channel boosting, and thus acapacitance component between the semiconductor pillar 75B and the wordline WLU is reduced. As a result, a load current caused by thecapacitance component between the word line and the upper semiconductorpillar is reduced.

In the same manner as in the example illustrated in FIG. 23, at a timepoint t15 e and a time point t16 e, the respective wirings are disabled.

As mentioned above, reading of data from the memory cell of the lowerarray layer 110A in the flash memory of the present embodiment isfinished.

Even if a read operation is performed in a state in which the voltageVSRC higher than the ground voltage VSS is applied to the source line SL(CELSRC), the flash memory of the present embodiment can perform a readoperation using the voltage sensing method.

As mentioned above, the flash memory of the present embodiment canimprove operation characteristics in the same manner as in theabove-described embodiments.

(7) Seventh Embodiment

With reference to FIG. 25, a memory device and a control method thereforaccording to a seventh embodiment will be explained. FIG. 25 is adiagram illustrating voltage waveforms of the respective wirings duringa read operation (or a verification operation) of a flash memory of thepresent embodiment.

In a read operation of the flash memory using the current sensingmethod, timings for controlling a voltage of a word line may bedifferent between an array layer including a selected word line and anarray layer not including the selected word line even if data is read ina state in which the voltage VSRC is applied to the source line SL(CELSRC). Some word lines of a selected block are disabled during aninitial operation, and thus an amount of a cell current generated in theselected block is reduced. As a result, the flash memory of the presentembodiment can reduce power consumption.

Read Operation on Memory Cell of Upper Array Layer

With reference to FIG. 25, a read operation on a memory cell of theupper array layer according to the current sensing method in the flashmemory of the present embodiment will be explained.

Time Point t1 f

As illustrated in FIG. 25, at a time point t1 f, the voltage VSG isapplied to the drain side select gate lines SGD-S and SGD-US, and theintermediate select gate lines SGM-S. The voltage VSRC is applied to thesource side select gate lines SGS-S and SGS-US, and the non-selectedintermediate select gate lines SGM-US.

The voltage VSRC is applied to the source line SL (CELSRC) and the bitline BL. A potential of the gate of the transistor is substantially thesame as a potential of the source or the drain thereof, and thus theselect transistors ST2 and ST3 of which the voltage VSRC is applied tothe gates are maintained to be turned off.

Time Point t2 f

If the word line WLU of the upper array layer 110B is selected as a readoperation target, a voltage starts to be applied to the word line WLU ata time point t2 f.

A potential of the word line WLL of the lower array layer 110A ismaintained to be ground voltage VSS. Since the memory cell of the lowerarray layer 110A is turned off, the source side select transistor ST2may be turned off. In this case, at the time point t1 f and the timepoint t2 f, the voltage VSRC is applied to the source side select gateline SGS-S of a selected string unit.

Time Point t3 f

At a time point t3 f, the reading voltage VCGRV for the selected wordline WL-S is controlled, and a voltage also starts to be applied to theword line (non-selected word line) WLL of the lower array layer 110A.

In the selected string unit, a potential of the source side select gateline SGS-S is increased from the voltage VSRC to the voltage VSG.

In a non-selected string unit, a potential of the non-selected drainside select gate line SGD-US is reduced from the voltage VSG to thevoltage VSRC. Consequently, the drain side select transistor ST1 of thenon-selected string unit is turned off.

In a period TA from the time point t2 f to the time point t3 f, residualelectric charge is released from the semiconductor pillars 75 to the bitline BL via the turned-on transistors ST1 and ST3 and memory cell MC. Inthe period TA, a potential of the word line WLL of the lower array layer110A is set to the ground voltage VSS, and thus the memory cell MC isturned off. The semiconductor pillar 75B of the upper array layer 110Bis electrically separated from the source line SL (CELSRC). In theperiod TA, even if a potential of the selected source side select gateline SGS-S is set to the voltage VSRC, an adverse effect on removal ofresidual electric charge in the semiconductor pillar 75B scarcelyoccurs.

Time Point t4 f to Time Point t6 f

After the bit line BL is charged in a period TB, in a period TC from atime point t4 f to a time point t5 f, the generation of a current in thebit line BL is sensed in a state in which a capacitance component (load)of the lower semiconductor pillar 75A of the non-selected string unit isreduced.

Thereafter, potentials of the respective wirings are set to the groundvoltage VSS.

Consequently, reading of data from the memory cell of the upper arraylayer 110B in the flash memory of the present embodiment is finished.

If the word line WLL of the lower array layer 110A is selected as areading target, potentials of the bit line BL, the source line SL(CELSRC), and the respective select gate lines SGS, SGD and SGM arecontrolled in the same manner as in the example illustrated in FIG. 22.

However, in the present embodiment, control of voltages for the wordlines WLL and WLU are different from the control in the exampleillustrated in FIG. 25. A voltage starts to be applied to the word lineWLL of the lower array layer 110A at the time point t2 f in FIG. 25.Application of the reading voltage VCGRV to the selected word line WL-Sand application of a voltage to the word line WLU of the upper arraylayer 110B are started at the time point t3 f in FIG. 25.

As mentioned above, a read operation on the memory cell of the lowerarray layer 110A is performed.

As mentioned above, as illustrated in FIG. 25, even if application of avoltage to each wiring is controlled, a release process on residualelectric charge in a semiconductor pillar of a selected block can beperformed, and thus a capacitance component of a non-selected stringunit can be reduced when data is read.

Therefore, the flash memory of the present embodiment can improveoperation characteristics in the same manner as in the above-describedembodiments.

(8) Eighth Embodiment

With reference to FIG. 26, a memory device and a control method thereforaccording to an eighth embodiment will be explained. FIG. 26 is adiagram illustrating voltage waveforms of the respective wirings duringa read operation (or a verification operation) of a flash memory of thepresent embodiment.

In a read operation of the flash memory using the voltage sensingmethod, timings for controlling a voltage of a word line may bedifferent between an array layer including a selected word line and anarray layer not including the selected word line even if data is read ina state in which the voltage VSRC is applied to the source line SL.

Operation Example

Read Operation on Memory Cell of Upper Array Layer

With reference to FIG. 26, a read operation on a memory cell of theupper array layer according to the voltage sensing method in the flashmemory of the present embodiment will be explained.

Time Point t11 f and Time Point t12 f

As illustrated in FIG. 26, in the same manner as in the above-describedexample (for example, the example illustrated in FIG. 23), at a timepoint t11 f, potentials of the select gate lines SGD, SGS and SGM, thebit line BL, and the source line SL (CELSRC) start to be controlled. Apotential of the source side select gate line SGS-S of a selected stringunit is set to the voltage VSRC.

Thereafter, if the word line WLU of the upper array layer 110B isselected, at the time point t11 f, a voltage starts to be applied to theword line WLU of the upper array layer 110B. A potential of the wordline WLL of the lower array layer 110A is maintained to be groundvoltage VSS.

Since the memory cell of the lower array layer 110A is turned off, theupper semiconductor pillar 75B is not connected to the source line SL(CELSRC). Therefore, in the selected string unit, a potential of thesource side select gate line SGS-S may be set to the voltage VSRC sothat the select transistor ST2 is turned off.

In a period TA, residual electric charge is released to the bit line BLfrom the semiconductor pillars 75 via the turned-on transistors.

Time Point t13 f

At the time point t13 f, the bit line BL starts to be charged. Apotential of the non-selected drain side select gate line SGD-US of anon-selected string unit is reduced from the voltage VSG to the voltageVSRC.

The reading pass voltage VREAD is applied to the word line WLL of thelower array layer 110A. A potential of the selected word line WL-S ofthe upper array layer 110B is reduced to the reading voltage VCGRV.

Time Point t14 f to Time Point t16 f

After a period TB elapses, at a time point t14 f, in the selected stringunit, a potential of the source side select gate line SGS-S is increasedfrom the voltage VSRC to the voltage VSG. Consequently, in the selectedstring unit, the select transistor ST2 is turned on, and thus thesemiconductor pillar 75A is electrically connected to the source line SL(CELSRC).

In a period TC, a state of a potential of the bit line BL is sensed in astate in which the lower semiconductor pillar 75A of the non-selectedstring unit is subject to channel boosting. Thus, data held in thememory cell is read. In the period TC, potentials of the select gatelines SGD-US, SGM-US and SGS-US of the non-selected string unit aremaintained to be the voltage VSRC.

Thereafter, at a time point t15 f and a time point t16 f, potentials ofthe respective wirings are set to the ground voltage VSS.

As mentioned above, the data read operation on the memory cell of theupper array layer 110B is completed.

Read Operation on Lower Array Layer

If the word line WLL of the lower array layer 110A is selected as areading target, potentials of the bit line BL, the source line SL(CELSRC), and the respective select gate lines SGS, SGD and SGM arecontrolled in the same manner as in the example illustrated in FIG. 24.

However, in the present embodiment, control of voltages for the wordlines WLL and WLU are different from the control in the exampleillustrated in FIG. 26. A voltage starts to be applied to the word lineWLL of the lower array layer 110A at the time point t12 f in FIG. 26.Application of the voltage VCGRV to the selected word line WL-S andapplication of a voltage to the word line WLU of the upper array layer110B are started at the time point t13 f in FIG. 26.

As mentioned above, a data read operation on the memory cell of thelower array layer 110A is performed.

As illustrated in FIG. 26, even if application of a voltage to eachwiring is controlled, a release process on residual electric charge in asemiconductor pillar of a selected block can be performed, and thus acapacitance component of a non-selected string unit and a load caused bythe capacitance component can be reduced when data is read.

Therefore, the flash memory of the present embodiment can improveoperation characteristics in the same manner as in the above-describedembodiments.

(9) Ninth Embodiment

With reference to FIGS. 27 and 28, a memory device and a control methodtherefor according to a ninth embodiment will be explained.

As illustrated in FIGS. 27 and 28, the lower array layer 110A and theupper array layer 110B respectively include intermediate select gatelines SGMU and SGML. In this case, a potential of the intermediateselect gate line SGM of the lower array layer 110A and a potential ofthe intermediate select gate line SGM of the upper array layer 110B maybe controlled separately from each other.

Hereinafter, For clarity purpose, the intermediate select gate line ofthe lower array layer 110A is referred to as a lower intermediate selectgate line SGML (SGML-S or SGML-US), and the intermediate select gateline of the upper array layer 110B is referred to as an upperintermediate select gate line SGMU (SGMU-S or SGMU-US).

Operation Example

Hereinafter, with reference to FIGS. 27 and 28, an operation example ofthe flash memory of the present embodiment will be described. Forexample, in the present embodiment, the flash memory performs a readoperation according to the current sensing method.

Read Operation on Upper Array Layer

FIG. 27 is a voltage waveform diagram for explaining reading of datafrom a memory cell of the upper array layer in a read operation of theflash memory of the present embodiment.

Time Point t1 g

As described above, at a time point t0, the sequencer 19 starts a readoperation. One of a plurality of word lines WLU of the upper array layer110B is set as a selected word line WL-S based on a selection address.

As illustrated in FIG. 27, at a time point tlg, the row control circuit12 applies the voltage VSG to the select gate lines SGD-S, SGS-S, SGMU-Sand SGML-S of a selected string unit.

With respect to a non-selected string unit, the row control circuit 12applies the voltage VSG to the non-selected drain side select gate lineSGD-US, and applies the ground voltage VSS to the non-selected sourceside select gate line SGS-US.

In the present embodiment, if data reading on the memory cell of theupper array layer 110B is performed, the row control circuit 12 appliesthe ground voltage VSS to the intermediate select gate line SGMU-US ofthe upper array layer 110B including the selected word line WL-S of thetwo intermediate select gate lines SGMU-US and SGML-US, and applies thevoltage VSG to the intermediate select gate line SGML-US of the lowerarray layer 110A, with respect to each of the non-selected string units.

Consequently, in the non-selected string unit, the select transistorST3U connected to the intermediate select gate line SGMU-US is turnedoff, and the select transistor ST3L connected to the intermediate selectgate line SGML-US is turned on. The turned-off select transistor ST3U isincluded in the same array layer 110B as the selected word line WL-S,and the turned-on intermediate select transistor ST3L is included in thearray layer 110A differently from the selected word line WL-S.

Time Point t2 g to Time Point t3 g

At a time point t2 g, voltages start to be applied to the word lines WLUand WLL. In a period TA, electric charges in the semiconductor pillars75A and 75B of the selected string unit and electric charge in the uppersemiconductor pillar 75B of the non-selected string unit are released tothe bit line BL or the source line SL (CELSRC) via the turned-on selecttransistors.

At a time point t3 g, the bit line BL starts to be charged. Among theword lines WLU, the selected word line WL-S is controlled so that apotential of the selected word line WL-S is set to the reading voltageVCGRV.

In the non-selected string unit, a potential of the non-selected drainside select gate line SGD-US is reduced from the voltage VSG to theground voltage VSS.

Time Point t4 g to Time Point t6 g

After the potential of the selected word line WL-S reaches the readingvoltage VCGRV, at a time point t4 g, a current of the bit line BL issensed in a state in which a part (here, the lower semiconductor pillar75A) of the semiconductor pillars 75 of the non-selected string unit issubject to channel boosting. In the present embodiment, in the samemanner as in the above-described example, a load caused by a capacitancecomponent of the semiconductor pillar is reduced, and thus data held inthe memory cell is determined.

Thereafter, at a time point t5 g and a time point t6 g, potentials ofthe respective wirings are set to the ground voltage VSS through controlof the potentials of the respective wirings.

As mentioned above, reading of data from the memory cell of the upperarray layer in the flash memory of the present embodiment is finished.

Read Operation on Memory Cell of Lower Array Layer FIG. 28 is a voltagewaveform diagram for explaining reading of data from a memory cell ofthe lower array layer in a read operation of the flash memory of thepresent embodiment.

Time Point t1 h

In the same manner as in the example illustrated in FIG. 27, at a timepoint t0, the sequencer 19 starts a read operation. One of a pluralityof word lines WLL of the lower array layer 110A is set as a selectedword line WL-S based on a selection address.

At a time point t1 h, the row control circuit 12 applies the voltage VSGto the select gate lines SGD-S, SGS-S, SGMU-S and SGML-S of a selectedstring unit.

With respect to a non-selected string unit, the ground voltage VSS isapplied to the non-selected drain side select gate line SGD-US, and thevoltage VSG is applied to the non-selected source side select gate lineSGS-US.

If data reading on the memory cell of the lower array layer 110A isperformed, unlike in the example illustrated in FIG. 27, the voltage VSGis applied to the intermediate select gate line SGMU-US of the upperarray layer 110B, and the ground voltage VSS is applied to theintermediate select gate line SGML-US of the lower array layer 110Aincluding the selected word line, with respect to each of thenon-selected string units.

Consequently, in the non-selected string unit, the select transistorST3U of the upper array layer 110B is turned on, and the selecttransistor ST3L of the lower array layer 110A is turned off. Theturned-on select transistor ST3U is included in the array layer 110Bdifferently from the selected word line, and the turned-off intermediateselect transistor ST3L is included in the same array layer 110A as theselected word line WL-S.

Time Point t2 h to Time Point t3 h

At a time point t2 h, voltages start to be applied to the word lines WLUand WLL.

In a period TA, an electric charge in the semiconductor pillars 75 isreleased to the bit line BL or the source line SL (CELSRC).

At a time point t3 h, the bit line BL starts to be charged. The selectedword line WL-S of the lower array layer 110A is controlled to be set tothe reading voltage VCGRV. In the non-selected string unit, a potentialof the non-selected source side select gate line SGS-US is reduced fromthe voltage VSG to the ground voltage VSS.

Time Point t4 h to Time Point t6 h

After the potential of the selected word line WL-S reaches the readingvoltage VCGRV, at a time point t4 h, a current of the bit line BL issensed. Consequently, a load caused by a capacitance component of thesemiconductor pillar is reduced, and, in this state, data held in thememory cell is determined.

Thereafter, at a time point t5 h and a time point t6 h, potentials ofthe respective wirings are set to the ground voltage VSS through controlof the potentials of the respective wirings.

Consequently, reading of data on the lower array layer in the flashmemory of the present embodiment is finished.

The operations illustrated in FIGS. 27 and 28 may be applied to averification operation.

In the present embodiment, in the read operations illustrated in FIGS.27 and 28, a potential of the source line SL (CELSRC) may be set to thevoltage VSRC higher than the ground voltage VSS in the same manner as inthe examples illustrated in FIGS. 21 and 22. In the present embodiment,timings of applying a voltage to the word lines WL may differ betweenthe lower array layer 110A and the upper array layer 110B according toan array layer including the selected word line WL-S in the same manneras in the examples illustrated in FIGS. 19 and 25.

Summary

In the flash memory of the present embodiment, a plurality ofintermediate select gate lines of a string unit can be controlledseparately from each other.

In the period TA in which residual electric charge in the semiconductorpillar is released during the read operation, among the plurality ofintermediate select gate lines of a non-selected string unit, the groundvoltage VSS is applied to the intermediate select gate line SGML of anarray layer including a selected word line, and the voltage (a voltagefor turning on the transistor ST3) VSG is applied to the intermediateselect gate line of an array layer not including the selected word line.

The flash memory of the present embodiment can cause a region (a regionnear the junction) between the two intermediate select gate lines to besubject to channel boosting by turning on the select transistor ST3connected to the select gate lines SGM corresponding to one of the twointermediate select gate lines SGML and SGMU. Consequently, the flashmemory of the present embodiment can further reduce a load caused by aparasitic capacitance of the semiconductor pillar.

In the junction of the stacked semiconductor pillars 75A and 75B, adistance between the lowermost conductive layer of the upper array layer110B and the uppermost conductive layer of the lower array layer 110A islonger than a distance (gap) between the word lines adjacent to eachother in the same array layer. The upper end of the semiconductor pillaris different from the lower end of the semiconductor pillar due to amanufacturing process, and thus a shape around the junction 999 is notuniform. Thus, a relatively large potential gradient may easily occurnear the junction 999. There is a probability that a hot carrier may begenerated in the junction 999 due to this potential gradient.

The hot carrier generated in the junction 999 hardly reaches an arraylayer including a selected word line since the transistor ST3 connectedto the select gate line SGM of the array layer 110 including theselected word line WL-S is turned off, and a length of the junction 999between the stacked intermediate select gate lines SGM is relativelylarge.

As a result, the flash memory of the present embodiment can prevent hotcarrier generation type reading disturbance.

As mentioned above, the flash memory of the present embodiment canimprove operation characteristics.

(10) Tenth Embodiment

With reference to FIGS. 29 and 30, a memory device and a control methodtherefor according to a tenth embodiment will be explained.

In the flash memory performing a read operation using the voltagesensing method, the intermediate select gate line SGMU of the upperarray layer 110B and the intermediate select gate line SGML of the lowerarray layer 110A may be controlled separately from each other.

Operation Example

Read Operation on Upper Array Layer

FIG. 29 is a voltage waveform diagram for explaining reading of datafrom a memory cell of the upper array layer in a read operation of theflash memory of the present embodiment.

Time Point t11 g

As illustrated in FIG. 28, when a read operation is started (time pointt0), a word line WLU of the upper array layer 110B is set as a selectedword line WL-S based on a selection address.

At a time point t11 g, the row control circuit 12 applies the voltageVSG to the select gate lines SGD-S, SGS-S, SGMU-S and SGML-S of aselected string unit.

With respect to a non-selected string unit, the voltage VSG is appliedto the non-selected drain side select gate line SGD-US, and the groundvoltage VSS is applied to the non-selected source side select gate lineSGS-US.

In the present embodiment, with respect to the non-selected string unit,the ground voltage VSS is applied to the intermediate select gate lineSGMU-US of the upper array layer 110B, and the voltage VSG is applied tothe intermediate select gate line SGML-US of the lower array layer 110A.

Consequently, in the non-selected string unit, the select transistorST3U of the array layer 110A including the selected word line WL-S isturned off, and the select transistor ST3L of the array layer 110B notincluding the selected word line WL-S is turned on.

Time Point t12 g to Time Point t13 g

At a time point t12 g, voltages start to be applied to the word linesWLU and WLL.

After electric charge is released in a period TA, at a time point t13 g,the bit line BL starts to be charged. The selected word line WL-S of theupper array layer 110B is controlled so that a potential of the selectedword line WL-S is set to the reading voltage VCGRV. A potential of thesource side select gate line SGS-S is reduced from the voltage VSG tothe ground voltage VSS.

In the non-selected string unit, a potential of the drain side selectgate line SGD-US is reduced from the voltage VSG to the ground voltageVSS. A potential of the intermediate select gate line SGML-US ismaintained to be the voltage VSG.

Time Point t14 g to Time Point t16 g

After the potential of the selected word line WL-S reaches the readingvoltage VCGRV, at a time point t14 g, the voltage VSG is applied to thesource side select gate line SGS-S in the selected string unit. Thelower semiconductor pillar 75A is applied to the source line SL (CELSRC)via the turned-on select transistor ST2. A potential of the bit line BLis sensed. As mentioned above, data held in the memory cell isdetermined in a state in which the lower semiconductor pillar 75A of thenon-selected string unit is subject to channel boosting.

Thereafter, in the same manner as in the above-described operationexamples, at a time point t15 g and a time point t16 g, potentials ofthe respective wirings are set to the ground voltage VSS through controlof the potentials of the respective wirings.

As mentioned above, reading of data from the memory cell of the upperarray layer 110B in the flash memory of the present embodiment isfinished.

Read Operation on Memory Cell of Lower Array Layer

FIG. 30 is a voltage waveform diagram for explaining reading of datafrom a memory cell of the lower array layer 110A in a read operation ofthe flash memory of the present embodiment.

Time Point t11 h

In the same manner as in the example illustrated in FIG. 29, at a timepoint t0, a word line WLL of the lower array layer 110A is set as aselected word line WL-S based on a selection address.

At a time point t11 h, the voltage VSG is applied to the select gatelines SGD-S, SGS-S, SGMU-S and SGML-S of a selected string unit.

With respect to a non-selected string unit, the ground voltage VSS isapplied to the drain side select gate line SGD-US, and the voltage VSGis applied to the non-selected source side select gate line SGS-US. Ifdata reading on the memory cell of the lower array layer 110A isperformed, unlike in the example illustrated in FIG. 29, the voltage VSGis applied to the intermediate select gate line SGMU-US, and the groundvoltage VSS is applied to the intermediate select gate line SGML-US,with respect to each of the non-selected string units.

Consequently, in the non-selected string unit, the select transistorST3U of the upper array layer 110B is turned on, and the selecttransistor ST3L of the lower array layer 110A including the selectedword line WL-S is turned off.

Time Point t12 h to Time Point t13 h

At a time point t12 h, voltages start to be applied to the word linesWLU and WLL.

After residual electric charge in the semiconductor pillars is released,at a time point t13 h, the bit line BL starts to be charged, and theselected word line WL-S of the lower array layer 110A is controlled tobe set to the reading voltage VCGRV.

In the selected and non-selected string units, potentials of the sourceside select gate lines SGS-S and SGS-US are set to the ground voltageVSS.

Time Point t14 h to Time Point t16 h

At a time point t14 h, the potential of the selected word line WL-Sreaches the reading voltage VCGRV, and then a potential of the sourceside select gate line SGS-S is set to the voltage VSG.

A potential of the bit line BL is sensed in a state in which the uppersemiconductor pillar 75B of the non-selected string unit is subject tothe channel boosting. Consequently, data held in the memory cell isdetermined.

Thereafter, at a time point t15 h and a time point t16 h, potentials ofthe respective wirings are set to the ground voltage VSS through controlof the potentials of the respective wirings.

Consequently, reading of data on the lower array layer in the flashmemory of the present embodiment is finished.

As in the present embodiment, even if the flash memory performs a readoperation using the voltage sensing method, the flash memory of thepresent embodiment can achieve the same effect as the effect in theninth embodiment.

The control of a timing of enabling a non-selected word line as in FIGS.20 and 26, and the control of a potential of the source line as in FIGS.23 and 24 may be applied to the flash memory of the present embodiment.

(11) Modification Examples

With reference to FIGS. 31 to 34, modification examples of the memorydevices and the control methods therefor according to the embodimentswill be explained.

(a) Modification Example 1 Structure Example

FIG. 31 is a schematic sectional view for explaining a structure of aflash memory according to a modification example of the embodiments.

As illustrated in FIG. 31, in a memory cell array of the flash memoryaccording to the modification example, a block may include three or morearray layers 110A, 110B and 110X.

The three array layers 110A, 110B and 110X are stacked in a verticaldirection to a surface of a substrate. The array layer 110X providedbetween the lower array layer 110A and the upper array layer 110B willbe referred to as an intermediate array layer 110X.

The intermediate array layer 110X includes a plurality of semiconductorpillars (hereinafter, referred to as intermediate semiconductor pillars)75X. A lower end of the semiconductor pillar 75X comes into contact withthe upper end of the lower semiconductor pillar 75A, and an upper end ofthe semiconductor pillar 75X comes into contact with the lower end ofthe upper semiconductor pillar 75B.

For example, the intermediate array layer 110X includes intermediateselect gate lines SGM0 b and SGMlb on an upper part (upper array layerside) in the intermediate array layer 110X, and includes intermediateselect gate lines SGM0 c and SGM1 c on a lower part (lower array layerside) in the intermediate array layer 110X.

The intermediate select gate lines SGM0 b and SGM1 b are provided in aboundary region between the upper array layer 110B and the intermediatearray layer 110X. The intermediate select gate lines SGM0 c and SGM1 care provided in a boundary region between the lower array layer 110A andthe intermediate array layer 110X.

In the intermediate array layer 110X, conductive layers 71 between theintermediate select gate lines SGM0 b and SGM0 c function like wordlines WL. Conductive layers 71 between the intermediate select gatelines SGM1 b and SGM1 c also function like word lines WL. Some of theword lines WL of the intermediate array layer 110X may be used as dummyword lines.

Hereinafter, the intermediate select gate lines SGM of the upper arraylayer 110B are referred to as intermediate select gate lines SGM0 a andSGM1 a. The intermediate select gate lines SGM of the lower array layer110A are referred to as intermediate select gate lines SGM0 d and SGM1d.

In the respective string units SU, potentials of the intermediate selectgate lines SGM of the array layers 110A, 110B and 110X can be controlledseparately from each other. Consequently, electrical connection betweenthe intermediate array layer 110X and the upper array layer 110B, andelectrical connection between the intermediate array layer 110X and theupper array layer 110B can be controlled separately from each other.

Operation Example

With reference to FIGS. 31 and 32, a description will be made of anoperation example of the flash memory of the present modificationexample. FIGS. 31 and 32 are diagrams schematically illustrating anoperation example of the flash memory of the present modificationexample. In this example, timings of controlling potentials ofrespective wirings in a read operation of the flash memory aresubstantially the same as the timings in the operation examplesdescribed in the first to tenth embodiments. Here, a description will bemade of a relationship between potentials of the respective intermediateselect gate lines SGM in the above-described read operation period(electric charge release period) TA in the flash memory.

FIG. 31 schematically illustrates a relationship between the respectiveintermediate select gate lines SGM in a read operation if the word lineWL of the upper array layer 110B is selected. In FIG. 31, the stringunit SU0 is selected an operation target.

As illustrated in FIG. 31, in the period TA from starting of control ofpotentials of the select gate lines to starting of application of areading voltage to the selected word line WL-S, the voltage VSG havingan “H” level are applied to the respective select gate lines SGD0, SGS0and SGM0 (SGM0 a to SGM0 d) of the selected string unit SU0, and thusthe select transistors ST1, ST2 and ST3 are turned on.

In the period TA, in the non-selected string units SU2 and SU3, thevoltage VSG is applied to the drain side select gate lines SGD2 andSGD3, and thus the select transistors ST1 are turned on. Consequently,electric charge in the semiconductor pillars 75B of the upper arraylayer 110B is released to bit lines (not illustrated). As a result,reading disturbance is reduced.

At this time, in the non-selected string units SU2 and SU3, the groundvoltage VSS having an “L” level is applied to the intermediate selectgate lines SGM1 a, SGM1 b, SGM1 c and SGM1 d, and thus the selecttransistors ST3 are turned off.

Consequently, the semiconductor pillars 75A and 75X of the lower arraylayer 110A and the intermediate array layer 110X are electricallyseparated from the semiconductor pillars 75B of the upper array layer110B, the bit lines BL, and the source line SL (CELSRC).

Therefore, when data is read from memory cells of the upper array layer110B, the semiconductor pillars 75X of a portion 99X of the intermediatearray layer 110X and the semiconductor pillars 75A of a portion 99A ofthe lower array layer 110A are subject to channel boosting.

Consequently, loads caused by capacitance components of the upper andintermediate semiconductor pillars 75A and 75X are reduced.

Data is read from memory cells of the intermediate array layer 110X andthe lower array layer 110A through control similar thereto as follows.

FIG. 32A schematically illustrates a relationship between potentials ofthe respective intermediate select gate lines SGM during a readoperation if a word line WL of the intermediate array layer 110X isselected.

In the period TA, the voltage VSG having an “H” level is applied to theintermediate select gate lines SGM1 a and SGM1 b in the non-selectedstring units SU2 and SU3. Consequently, in the non-selected stringunits, not only the upper semiconductor pillars 75B but also theintermediate semiconductor pillars 75X are electrically connected to thebit lines (not illustrated). Consequently, electric charge in theintermediate semiconductor pillars 75X is released to the bit lines BL.As a result, reading disturbance is reduced.

In this case, when data is read from memory cells of the intermediatearray layer 110X, in the non-selected string units, semiconductorpillars 75A of the portion 99A of the lower array layer 110A are subjectto channel boosting, and thus loads caused by capacitance components ofthe lower semiconductor pillars 75A are reduced.

If the ground voltage VSS having an “L” level is applied to theintermediate select gate line SGM1 d of the lower array layer 110A, thevoltage VSG having an “H” level may be applied to the intermediateselect gate line SGM1 c.

Alternatively, in order to release electric charge in the semiconductorpillars 75X of the intermediate array layer 110X in the non-selectedstring units, the ground voltage VSS may be applied to the intermediateselect gate line SGM1 b on the upper array layer 110B side, and thevoltage VSG may be applied to the intermediate select gate line SGM1 con the lower array layer 110A side. In this case, in the non-selectedstring units, the voltage VSG is applied to the intermediate select gateline SGM1 d and the source side select gate line SGS1 of the lower arraylayer 110A, and the ground voltage VSS is applied to the drain sideselect gate lines SGM2 and SGM3 of the upper array layer 110B.

Consequently, electric charge in the semiconductor pillars 75X of theintermediate array layer 110X is released to the source line (notillustrated) via the semiconductor pillars 75A of the lower array layer110A.

FIG. 32B schematically illustrates a relationship between potentials ofthe respective intermediate select gate lines SGM during a readoperation if a word line WL of the lower array layer 110A is selected.

In the period TA, the ground voltage VSS is applied to the drain sideselect gate lines SGD1, SGD2 and SGD3, and the voltage VSG is applied tothe source side select gate lines SGS0 and SGS1, in the non-selectedstring units SU2 and SU3. Consequently, the semiconductor pillars 75 ofthe non-selected string units are electrically separated from the bitlines, and are electrically connected to the source line.

The ground voltage VSS having an “L” level is applied to thenon-selected intermediate select gate lines SGM1 a, SGM1 b, SGM1 c andSGM1 d. Consequently, in the non-selected string unit, the semiconductorpillars 75B and 75X of the upper array layer 110B and the intermediatearray layer 110X are electrically separated from the semiconductorpillars 75A of the lower array layer 110A.

Therefore, electric charge in the lower semiconductor pillars 75A isreleased to the source line, and thus reading disturbance is reduced.

When data is read from the memory cells of the lower array layer 110A,the semiconductor pillars 75B of the portion 99B of the upper arraylayer 110B and the semiconductor pillars 75X of the portion 99X of theintermediate array layer 110X are subject to channel boosting. As aresult, loads caused by capacitance components of the lower andintermediate semiconductor pillars 75A and 75X are reduced.

As in FIG. 32B, in order to release electric charge in the semiconductorpillars 75X of the intermediate array layer 110X, the voltage VSG havingan “H” level may be applied to the intermediate select gate lines SGM1 cand SGM1 d. In this case, the occurrence of reading disturbance isfurther reduced.

As in the present modification example, even if the memory cell array 11includes three array layers, some of the semiconductor pillars of thenon-selected string units in the selected block BK can be caused to besubject to channel boosting. Therefore, reading disturbance can bereduced, and a capacitance component during a read operation (or averification operation) can also be reduced.

Therefore, the flash memory of the present modification example canreduce power consumption and can thus suppress a decrease in anoperation speed.

(b) Modification Example 2

FIG. 33 is a diagram for explaining a structure of a flash memoryaccording to a modification example of the embodiments. FIG. 33illustrates a sectional structure of the flash memory according to thepresent modification example.

As illustrated in FIG. 33, the select gate lines SGD, SGS and SGM, theword lines WL, and the string units SU may be separately provided ineach of the string units SU. The source line contact CELSRC is providedbetween the string units. The respective string units SU do not sharethe select gate lines SGD, SGS and SGM.

In the example illustrated in FIG. 33, a single string unit correspondsto a single area FNG.

Even if the flash memory includes blocks having the structureillustrated in FIG. 33, the flash memory can perform each operationexample described in the first to tenth embodiments.

(c) Modification Example 3

FIGS. 34A to 34F are diagrams for explaining a structure of a flashmemory according to a modification example of the embodiments.

FIGS. 34A to 34F illustrate modification examples of a structure of astring unit including intermediate select gate lines in the flash memoryof the present embodiment.

As illustrated in FIG. 34A, an intermediate select gate line SGM of theupper array layer 110B and an intermediate select gate line SGM of thelower array layer 110A may be provided between a dummy word line DWLA ofthe lower array layer 110A and a dummy word line DWLB of the upper arraylayer 110B in the D3 direction.

As illustrated in FIG. 34B, in each of the array layers 110A and 110B,an intermediate select gate line SGM may be provided between two dummyword lines DWL in the D3 direction.

As illustrated in FIG. 34C, an array layer not including an intermediateselect gate line SGM may be provided in a block (memory cell array).

For example, in FIG. 34C, the upper array layer 110B includes theintermediate select gate line SGM, and the lower array layer 110A doesnot include the intermediate select gate line. The intermediate selectgate line SGM is provided between a dummy word line DWL of the upperarray layer 110B and a dummy word line DWL of the lower array layer 110Ain the D3 direction.

As illustrated in FIG. 34D, the upper array layer 110B does not includean intermediate select gate line SGM, and the lower array layer 110Aincludes the intermediate select gate line SGM.

As illustrated in FIGS. 34E and 34F, in an array layer including anintermediate select gate line SGM, the intermediate select gate line SGMmay be provided between two dummy word lines of the array layer.

As mentioned above, positions of the intermediate select gate lines SGMin the string unit, and layouts of the intermediate select gate linesSGM and the dummy word lines DWL may be changed as appropriate. Any oneof FIGS. 34A to 34F illustrating the structures of the NAND string 111may be applied to the flash memories of the first to tenth embodiments.

During a read operation of the flash memory, reading disturbance in anon-selected string unit may be reduced not only by electricallyseparating the stacked array layers 110A and 110B from each other usingthe intermediate select gate lines SGM but also by applying a voltage Vxlower than the voltage VSG to the dummy word lines DWL. The voltage Vxis higher than the ground voltage VSS.

In this case, in the same manner as the drain side select gate lines SGMor the intermediate select gate lines SGM, the dummy word lines DWL areelectrically separated from each other for each string unit or every twostring units.

(12) Others

If a flash memory used in the memory system of the present embodiment isa multi-value flash memory, a read operation of the multi-value flashmemory includes the following determination voltages.

A determination voltage applied to a selected word line in a readoperation at the A level is in a range of, for example, 0 V to 0.55 V.However, a determination voltage for the A level is not limited to therange, and may be any one of the ranges of 0.1 V to 0.24 V, 0.21 V to0.31 V, 0.31 V to 0.4 V, 0.4 V to 0.5 V, and 0.5 V to 0.55 V.

A determination voltage applied to a selected word line in a readoperation at the B level is in a range of, for example, 1.5 V to 2.3 V.However, a determination voltage for the B level is not limited to therange, and may be any one of the ranges of 1.65 V to 1.8 V, 1.8 V to1.95 V, 1.95 V to 2.1 V, and 2.1 V to 2.3 V.

A determination voltage applied to a selected word line in a readoperation at the C level is in a range of, for example, 3.0 V to 4.0 V.However, a determination voltage for the C level is not limited to therange, and may be any one of the ranges of 3.0 V to 3.2 V, 3.2 V to 3.4V, 3.4 V to 3.5V, 3.5 V to 3.6 V, and 3.6 V to 4.0 V.

A period (tR) of a read operation may be any one of, for example, 25 μsto 38 μs, 38 μs to 70 μs, and 70 μs to 80 μs.

A write operation of the multi-value flash memory includes a programoperation and a verification operation.

In the write operation of the multi-value flash memory, a voltage whichis initially applied to a selected word line during the programoperation is in a range of, for example, 13.7 V to 14.3 V. The voltageis not limited to this range, and may be either one of, for example,13.7 V to 14.0 V and 14.0 V to 14.6 V.

If the program operation is performed according to an incremental steppulse program (ISPP) method, a step-up voltage is, for example, about0.5 V.

A non-selection voltage (pass voltage) applied to a non-selected wordline has a value in a range of, for example, 6.0 V to 7.3 V. However, anon-selection voltage is not limited to this value, and may have a valuein a range of, for example, 7.3 V to 8.4 V, and may be equal to or lessthan 6.0 V.

A pass voltage to be applied may be changed depending on whether anon-selected word line is an odd-numbered word line or an even-numberedword line.

A period (tProg) of a write operation may be any one of, for example,1700 μs to 1800 μs, 1800 μs to 1900 μs, and 1900 μs to 2000 μs.

In an erasing operation of the multi-value flash memory, a voltageapplied to a well region which is formed on an upper part in asemiconductor substrate and above which a memory cell is disposed has avalue in a range of, for example, 12 V to 13.6 V. The voltage is notlimited to this value, and may have a value in any one of ranges, forexample, 13.6 V to 14.8 V, 14.8 V to 19.0 V, 19.0 V to 19.8 V, and 19.8V to 21 V.

A period (tErase) of the erasing operation may be one of ranges of, forexample, 3000 μs to 4000 μs, 4000 μs to 5000 μs, and 4000 μs to 9000 μs.

The memory cell has the charge storage layer which is disposed on theside surface of the semiconductor pillar via the tunnel insulating filmof 4 nm to 10 nm. The charge storage layer has a structure in which aninsulating film (for example, SiN or SiON) having a film thickness of 2nm to 3 nm, and polysilicon having a film thickness of 3 nm to 8 nm arelaminated. Polysilicon may contain a metal such as Ru.

The insulating film is formed on the charge storage layer. Theinsulating film includes a lower-layer high-k film having a thickness of3 nm to 10 nm, an upper-layer high-k film having a thickness of 3 nm to10 nm, and a silicon oxide film having a thickness of 4 to 10 nm. Thehigh-k film may be an HfO film. A thickness of the silicon oxide filmmay be larger than a thickness of the high-k film.

A control gate electrode having a film thickness of 30 nm to 70 nm isprovided on the insulating film via a material having a film thicknessof 3 nm to 10 nm. Such a material is a metal oxide film such as TaO, ora metal nitride film such as TaN. The control gate electrode may be ametal such as tungsten (W).

An air gap may be provided between the memory cells.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A memory device comprising: a first memory stringincluding a first memory cell, a second memory cell, a first selecttransistor above the first memory cell, a second select transistor belowthe second memory cell, and a third select transistor between the firstmemory cell and the second memory cell; a second memory string includinga third memory cell, a fourth memory cell, a fourth select transistorabove the third memory cell, a fifth select transistor below the fourthmemory cell, and a sixth select transistor between the third memory celland the fourth memory cell; a first word line electrically connected toa gate of the first memory cell and a gate of the third memory cell; asecond word line electrically connected to a gate of the second memorycell and a gate of the fourth memory cell; and a controller configuredto execute a read operation on one of the memory cells, the readoperation including a first phase and a second phase after the firstphase, wherein when a read target is one of the first memory cell andthe second memory cell, during the first phase, a first voltage isapplied to one of the first select transistor and the second selecttransistor, the third select transistor, and one of the fourth selecttransistor and the fifth select transistor, and a second voltage lowerthan the first voltage is applied to the sixth select transistor and theother one of the fourth select transistor and the fifth selecttransistor, and during the second phase, the first voltage is applied tothe first select transistor, the second select transistor and the thirdselect transistor, and the second voltage is applied to the fourthselect transistor, the fifth select transistor, and the sixth selecttransistor.
 2. The device according to claim 1, wherein, when the readtarget is the first memory cell, during the first phase, the firstvoltage is applied to the first, second, third, and fourth selecttransistors, and the second voltage is applied to the fifth and sixthselect transistors, and during the second phase, the second voltage isapplied to the fourth, fifth, and sixth select transistors, and a readtarget voltage is applied to the first word line.
 3. The deviceaccording to claim 1, wherein, when the read target is the second memorycell, during the first phase, the first voltage is applied to the first,second, third, and fifth select transistors, and the second voltage isapplied to the fourth and sixth select transistors, and during thesecond phase, the second voltage is applied to the fourth, fifth, andsixth select transistors, and a read target voltage is applied to thesecond word line.
 4. The device according to claim 1, wherein, when theread target is the first memory cell, during the first phase, the firstvoltage is applied to the first, second, and fourth select transistors,and the second voltage is applied to the fifth and sixth selecttransistors, and during the second phase, the first voltage is appliedto the third select transistor, the second voltage is applied to thefourth, fifth, and sixth select transistors, and a read target voltageis applied to the first word line.
 5. The device according to claim 1,wherein, when the read target is the second memory cell, during thefirst phase, the first voltage is applied to the second, third, andfifth select transistors, and the second voltage is applied to thefourth and sixth select transistors, and during the second phase, thefirst voltage is applied to the first select transistor, the secondvoltage is applied to the fourth, fifth, and sixth select transistors,and a read target voltage is applied to the second word line.
 6. Thedevice according to claim 1, wherein the controller is furtherconfigured to execute a program operation, and the read operation iscarried out after the program operation as a part of a verificationoperation.
 7. The device according to claim 1, wherein during the firstphase, the first voltage is applied to the second select transistor, andduring the second phase, the voltage applied to one of the first andsecond select transistors transitions from the first voltage to thesecond voltage, and thereafter transitions from the second voltage tothe first voltage.
 8. The device according to claim 1, wherein thesecond voltage is ground voltage.
 9. The device according to claim 1,wherein the second voltage is higher than ground voltage.
 10. The deviceaccording to claim 1, wherein the first memory string further includes:a fifth memory cell below the third select transistor, and a seventhselect transistor below the fifth memory cell and above the secondmemory cell, the second memory string further includes: a sixth memorycell below the fifth select transistor, and an eighth select transistorbelow the sixth memory cell and above the fourth memory cell, and a gateof the fifth memory cell and a gate of the sixth memory cell areelectrically connected via a third word line.
 11. The device accordingto claim 1, wherein, when the read target is the first memory cell,during the first phase, the first voltage is applied to the first,second, third, fourth, and seventh select transistors, and the secondvoltage is applied to the fifth, sixth, and eighth select transistors,and during the second phase, the second voltage is applied to thefourth, fifth, sixth, and eighth select transistors, and a read targetvoltage is applied to the first word line.
 12. A memory devicecomprising: a first memory string including a first memory cell, asecond memory cell, a first select transistor above the first memorycell, a second select transistor below the second memory cell, and thirdand fourth select transistors between the first and second memory cells;a second memory string including a third memory cell, a fourth memorycell, a fifth select transistor above the third memory cell, a sixthselect transistor below the fourth memory cell, and seventh and eighthselect transistors between the third and fourth memory cells; a firstword line electrically connected to gates of the first and third memorycells; a second word line electrically connected to gates of the secondand fourth memory cells; and a controller configured to execute a readoperation on one of the memory cells, the read operation including afirst phase and a second phase, wherein when a read target is one of thefirst and second memory cells, during the first phase, a first voltageis applied to the first, second, third, and fourth select transistors,one of the fifth and sixth select transistors, and one of the seventhand eighth select transistors, and a second voltage lower than the firstvoltage is applied to the other one of the fifth and sixth selecttransistors and the other one of the seventh and eighth selecttransistors, and during the second phase, the second voltage is appliedto the fifth and sixth select transistors, and the other one of theseventh and eighth select transistors, and the voltage applied to saidone of the seventh and eighth select transistors is maintained at thefirst voltage.
 13. The device according to claim 12, wherein, when theread target is the first memory cell, during the first phase, the firstvoltage is applied to the first, second, third, fourth, fifth, andeighth select transistors, and the second voltage is applied to thesixth and seventh select transistors, and during the second phase, thesecond voltage is applied to the fifth, sixth, and seventh selecttransistors, and a read target voltage is applied to the first wordline.
 14. The device according to claim 12, wherein at a beginning ofthe second phase, the voltage applied to the second select transistortransitions from the first voltage to the second voltage, and during thesecond phase, the voltage applied to the second select transistortransitions from the second voltage to the first voltage.
 15. The deviceaccording to claim 12, wherein, when the read target is the secondmemory cell, during the first phase, the first voltage is applied to thefirst, second, third, fourth, sixth, and seventh select transistors, andthe second voltage is applied to the fifth and eighth selecttransistors, and during the second phase, the second voltage is appliedto the fifth, sixth, and eighth select transistors, and a read targetvoltage is applied to the second word line.
 16. The device according toclaim 12, wherein at a beginning of the second phase, the voltageapplied to the second select transistor transitions from the firstvoltage to the second voltage, and during the second phase, the voltageapplied to the second select transistor transitions from the secondvoltage to the first voltage.
 17. The device according to claim 12,wherein the read operation is carried out during a program verifyoperation.
 18. The device according to claim 12, wherein the secondvoltage is ground voltage.